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 $183.37   13.130%   $207.4465   $207.45   $207.45   $207.40  
  Purchase #2 $148.85   3.204%   $153.6192   $153.62   $153.60   $153.60  
  Purchase #3 $65.82   4.771%   $68.9603   $68.96   $68.95   $69.00  
  Purchase #4 $246.32   9.390%   $269.4494   $269.45   $269.45   $269.40  
  Purchase #5 $249.92   5.692%   $264.1454   $264.15   $264.15   $264.10  
  Purchase #6 $57.62   4.423%   $60.1685   $60.17   $60.15   $60.20  
  Purchase #7 $92.62   7.370%   $99.4461   $99.45   $99.45   $99.40  
  7 purchase totals = $1,044.52       $1,123.2354   $1,123.25   $1,123.20   $1,123.10