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 $203.61   10.261%   $224.5024   $224.50   $224.50   $224.50  
  Purchase #2 $53.25   10.329%   $58.7502   $58.75   $58.75   $58.80  
  Purchase #3 $192.34   4.663%   $201.3088   $201.31   $201.30   $201.30  
  Purchase #4 $172.88   4.277%   $180.2741   $180.27   $180.25   $180.30  
  Purchase #5 $209.67   3.764%   $217.562   $217.56   $217.55   $217.60  
  Purchase #6 $247.40   10.281%   $272.8352   $272.84   $272.85   $272.80  
  Purchase #7 $142.36   11.283%   $158.4225   $158.42   $158.40   $158.40  
  7 purchase totals = $1,221.51       $1,313.6552   $1,313.65   $1,313.60   $1,313.70