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 $244.68   11.832%   $273.6305   $273.63   $273.65   $273.60  
  Purchase #2 $226.39   8.822%   $246.3621   $246.36   $246.35   $246.40  
  Purchase #3 $201.44   7.194%   $215.9316   $215.93   $215.95   $215.90  
  Purchase #4 $204.42   5.507%   $215.6774   $215.68   $215.70   $215.70  
  Purchase #5 $188.82   8.835%   $205.5022   $205.50   $205.50   $205.50  
  Purchase #6 $216.80   3.353%   $224.0693   $224.07   $224.05   $224.10  
  Purchase #7 $193.59   5.715%   $204.6537   $204.65   $204.65   $204.70  
  7 purchase totals = $1,476.14       $1,585.8268   $1,585.82   $1,585.85   $1,585.90