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 $95.58   4.536%   $99.9155   $99.92   $99.90   $99.90  
  Purchase #2 $182.81   9.383%   $199.9631   $199.96   $199.95   $200.00  
  Purchase #3 $76.97   11.159%   $85.5591   $85.56   $85.55   $85.60  
  Purchase #4 $148.66   12.832%   $167.7361   $167.74   $167.75   $167.70  
  Purchase #5 $243.42   10.714%   $269.5   $269.50   $269.50   $269.50  
  Purchase #6 $232.97   10.535%   $257.5134   $257.51   $257.50   $257.50  
  Purchase #7 $64.97   5.198%   $68.3471   $68.35   $68.35   $68.30  
  7 purchase totals = $1,045.38       $1,148.5343   $1,148.54   $1,148.50   $1,148.50