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 $201.69   8.633%   $219.1019   $219.10   $219.10   $219.10  
  Purchase #2 $96.43   8.506%   $104.6323   $104.63   $104.65   $104.60  
  Purchase #3 $186.55   9.765%   $204.7666   $204.77   $204.75   $204.80  
  Purchase #4 $111.71   13.464%   $126.7506   $126.75   $126.75   $126.80  
  Purchase #5 $229.86   8.741%   $249.9521   $249.95   $249.95   $250.00  
  Purchase #6 $197.49   7.530%   $212.361   $212.36   $212.35   $212.40  
  Purchase #7 $115.64   5.356%   $121.8337   $121.83   $121.85   $121.80  
  7 purchase totals = $1,139.37       $1,239.3982   $1,239.39   $1,239.40   $1,239.50