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 $58.96   6.317%   $62.6845   $62.68   $62.70   $62.70  
  Purchase #2 $173.77   5.459%   $183.2561   $183.26   $183.25   $183.30  
  Purchase #3 $132.68   13.651%   $150.7921   $150.79   $150.80   $150.80  
  Purchase #4 $55.81   6.333%   $59.3444   $59.34   $59.35   $59.30  
  Purchase #5 $235.83   12.619%   $265.5894   $265.59   $265.60   $265.60  
  Purchase #6 $109.45   9.620%   $119.9791   $119.98   $120.00   $120.00  
  Purchase #7 $215.62   4.793%   $225.9547   $225.95   $225.95   $226.00  
  7 purchase totals = $982.12       $1,067.6003   $1,067.59   $1,067.65   $1,067.70