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 $39.47   11.361%   $43.9542   $43.95   $43.95   $44.00  
  Purchase #2 $177.43   13.811%   $201.9349   $201.93   $201.95   $201.90  
  Purchase #3 $55.26   4.191%   $57.5759   $57.58   $57.60   $57.60  
  Purchase #4 $76.82   6.507%   $81.8187   $81.82   $81.80   $81.80  
  Purchase #5 $56.31   12.678%   $63.449   $63.45   $63.45   $63.40  
  Purchase #6 $16.68   10.516%   $18.4341   $18.43   $18.45   $18.40  
  Purchase #7 $8.73   6.569%   $9.3035   $9.30   $9.30   $9.30  
  7 purchase totals = $430.70       $476.4703   $476.46   $476.50   $476.40