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 $56.51   5.340%   $59.5276   $59.53   $59.55   $59.50  
  Purchase #2 $248.34   4.821%   $260.3125   $260.31   $260.30   $260.30  
  Purchase #3 $173.94   9.818%   $191.0174   $191.02   $191.00   $191.00  
  Purchase #4 $235.37   8.430%   $255.2117   $255.21   $255.20   $255.20  
  Purchase #5 $219.68   7.870%   $236.9688   $236.97   $236.95   $237.00  
  Purchase #6 $99.70   6.571%   $106.2513   $106.25   $106.25   $106.30  
  Purchase #7 $143.49   13.514%   $162.8812   $162.88   $162.90   $162.90  
  7 purchase totals = $1,177.03       $1,272.1705   $1,272.17   $1,272.15   $1,272.20