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 $165.32   11.294%   $183.9912   $183.99   $184.00   $184.00  
  Purchase #2 $86.68   7.218%   $92.9366   $92.94   $92.95   $92.90  
  Purchase #3 $196.40   8.762%   $213.6086   $213.61   $213.60   $213.60  
  Purchase #4 $59.93   7.677%   $64.5308   $64.53   $64.55   $64.50  
  Purchase #5 $163.56   12.597%   $184.1637   $184.16   $184.15   $184.20  
  Purchase #6 $158.89   5.594%   $167.7783   $167.78   $167.80   $167.80  
  Purchase #7 $148.38   4.525%   $155.0942   $155.09   $155.10   $155.10  
  7 purchase totals = $979.16       $1,062.1034   $1,062.10   $1,062.15   $1,062.10