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 $96.35   11.753%   $107.674   $107.67   $107.65   $107.70  
  Purchase #2 $26.65   6.166%   $28.2932   $28.29   $28.30   $28.30  
  Purchase #3 $59.33   6.354%   $63.0998   $63.10   $63.10   $63.10  
  Purchase #4 $8.32   11.822%   $9.3036   $9.30   $9.30   $9.30  
  Purchase #5 $142.38   8.790%   $154.8952   $154.90   $154.90   $154.90  
  Purchase #6 $158.36   9.555%   $173.4913   $173.49   $173.50   $173.50  
  Purchase #7 $124.92   6.459%   $132.9886   $132.99   $133.00   $133.00  
  7 purchase totals = $616.31       $669.7457   $669.74   $669.75   $669.80