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 $204.61   11.792%   $228.7376   $228.74   $228.75   $228.70  
  Purchase #2 $45.79   9.767%   $50.2623   $50.26   $50.25   $50.30  
  Purchase #3 $59.32   6.456%   $63.1497   $63.15   $63.15   $63.10  
  Purchase #4 $237.98   9.617%   $260.8665   $260.87   $260.85   $260.90  
  Purchase #5 $126.75   13.370%   $143.6965   $143.70   $143.70   $143.70  
  Purchase #6 $222.61   10.269%   $245.4698   $245.47   $245.45   $245.50  
  Purchase #7 $225.89   12.499%   $254.124   $254.12   $254.10   $254.10  
  7 purchase totals = $1,122.95       $1,246.3064   $1,246.31   $1,246.25   $1,246.30