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 $90.25   3.698%   $93.5874   $93.59   $93.60   $93.60  
  Purchase #2 $175.82   12.209%   $197.2859   $197.29   $197.30   $197.30  
  Purchase #3 $147.49   10.298%   $162.6785   $162.68   $162.70   $162.70  
  Purchase #4 $151.61   10.785%   $167.9611   $167.96   $167.95   $168.00  
  Purchase #5 $151.44   6.647%   $161.5062   $161.51   $161.50   $161.50  
  Purchase #6 $247.30   10.716%   $273.8007   $273.80   $273.80   $273.80  
  Purchase #7 $62.39   12.700%   $70.3135   $70.31   $70.30   $70.30  
  7 purchase totals = $1,026.30       $1,127.1333   $1,127.14   $1,127.15   $1,127.20