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 $232.83   13.368%   $263.9547   $263.95   $263.95   $264.00  
  Purchase #2 $150.85   10.343%   $166.4524   $166.45   $166.45   $166.50  
  Purchase #3 $225.63   12.138%   $253.017   $253.02   $253.00   $253.00  
  Purchase #4 $99.50   6.500%   $105.9675   $105.97   $105.95   $106.00  
  Purchase #5 $130.86   7.397%   $140.5397   $140.54   $140.55   $140.50  
  Purchase #6 $29.67   12.408%   $33.3515   $33.35   $33.35   $33.40  
  Purchase #7 $123.61   11.806%   $138.2034   $138.20   $138.20   $138.20  
  7 purchase totals = $992.95       $1,101.4862   $1,101.48   $1,101.45   $1,101.60