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 $62.92   6.404%   $66.9494   $66.95   $66.95   $66.90  
  Purchase #2 $194.92   12.170%   $218.6418   $218.64   $218.65   $218.60  
  Purchase #3 $201.61   13.373%   $228.5713   $228.57   $228.55   $228.60  
  Purchase #4 $238.66   5.334%   $251.3901   $251.39   $251.40   $251.40  
  Purchase #5 $152.77   10.355%   $168.5893   $168.59   $168.60   $168.60  
  Purchase #6 $107.99   11.358%   $120.2555   $120.26   $120.25   $120.30  
  Purchase #7 $223.73   6.702%   $238.7244   $238.72   $238.70   $238.70  
  7 purchase totals = $1,182.60       $1,293.1218   $1,293.12   $1,293.10   $1,293.10