Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $161.26   13.616%   $183.2172   $183.22   $183.20   $183.20  
  Purchase #2 $107.97   9.148%   $117.8471   $117.85   $117.85   $117.80  
  Purchase #3 $239.46   8.394%   $259.5603   $259.56   $259.55   $259.60  
  Purchase #4 $120.59   10.765%   $133.5715   $133.57   $133.55   $133.60  
  Purchase #5 $194.46   4.510%   $203.2301   $203.23   $203.25   $203.20  
  Purchase #6 $139.35   5.439%   $146.9292   $146.93   $146.95   $146.90  
  Purchase #7 $107.49   13.464%   $121.9625   $121.96   $121.95   $122.00  
  7 purchase totals = $1,070.58       $1,166.3179   $1,166.32   $1,166.30   $1,166.30