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 $73.71   9.376%   $80.621   $80.62   $80.60   $80.60  
  Purchase #2 $232.46   6.290%   $247.0817   $247.08   $247.10   $247.10  
  Purchase #3 $62.96   6.645%   $67.1437   $67.14   $67.15   $67.10  
  Purchase #4 $240.39   4.213%   $250.5176   $250.52   $250.50   $250.50  
  Purchase #5 $104.48   3.144%   $107.7649   $107.76   $107.75   $107.80  
  Purchase #6 $81.50   5.819%   $86.2425   $86.24   $86.25   $86.20  
  Purchase #7 $123.38   9.601%   $135.2257   $135.23   $135.25   $135.20  
  7 purchase totals = $918.88       $974.5971   $974.59   $974.60   $974.50