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 $58.68   11.433%   $65.3889   $65.39   $65.40   $65.40  
  Purchase #2 $189.99   6.614%   $202.5559   $202.56   $202.55   $202.60  
  Purchase #3 $114.95   10.758%   $127.3163   $127.32   $127.30   $127.30  
  Purchase #4 $67.52   13.700%   $76.7702   $76.77   $76.75   $76.80  
  Purchase #5 $116.25   11.839%   $130.0128   $130.01   $130.00   $130.00  
  Purchase #6 $127.89   3.227%   $132.017   $132.02   $132.00   $132.00  
  Purchase #7 $11.49   5.182%   $12.0854   $12.09   $12.10   $12.10  
  7 purchase totals = $686.77       $746.1465   $746.16   $746.10   $746.20