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 $85.55   3.647%   $88.67   $88.67   $88.65   $88.70  
  Purchase #2 $190.36   5.229%   $200.3139   $200.31   $200.30   $200.30  
  Purchase #3 $116.83   3.484%   $120.9004   $120.90   $120.90   $120.90  
  Purchase #4 $101.45   10.587%   $112.1905   $112.19   $112.20   $112.20  
  Purchase #5 $81.46   7.243%   $87.3601   $87.36   $87.35   $87.40  
  Purchase #6 $160.88   3.814%   $167.016   $167.02   $167.00   $167.00  
  Purchase #7 $210.26   6.803%   $224.564   $224.56   $224.55   $224.60  
  7 purchase totals = $946.79       $1,001.0149   $1,001.01   $1,000.95   $1,001.10