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 $39.42   4.857%   $41.3346   $41.33   $41.35   $41.30  
  Purchase #2 $60.42   8.250%   $65.4047   $65.40   $65.40   $65.40  
  Purchase #3 $86.34   9.419%   $94.4724   $94.47   $94.45   $94.50  
  Purchase #4 $72.57   4.365%   $75.7377   $75.74   $75.75   $75.70  
  Purchase #5 $48.67   12.696%   $54.8491   $54.85   $54.85   $54.80  
  Purchase #6 $31.44   11.325%   $35.0006   $35.00   $35.00   $35.00  
  Purchase #7 $209.66   13.497%   $237.9578   $237.96   $237.95   $238.00  
  7 purchase totals = $548.52       $604.7569   $604.75   $604.75   $604.70