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 $208.58   9.132%   $227.6275   $227.63   $227.65   $227.60  
  Purchase #2 $125.75   13.595%   $142.8457   $142.85   $142.85   $142.80  
  Purchase #3 $227.43   3.421%   $235.2104   $235.21   $235.20   $235.20  
  Purchase #4 $200.85   7.667%   $216.2492   $216.25   $216.25   $216.20  
  Purchase #5 $226.56   7.679%   $243.9575   $243.96   $243.95   $244.00  
  Purchase #6 $53.25   11.848%   $59.5591   $59.56   $59.55   $59.60  
  Purchase #7 $45.88   5.721%   $48.5048   $48.50   $48.50   $48.50  
  7 purchase totals = $1,088.30       $1,173.9542   $1,173.96   $1,173.95   $1,173.90