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 $202.40   10.688%   $224.0325   $224.03   $224.05   $224.00  
  Purchase #2 $98.81   8.117%   $106.8304   $106.83   $106.85   $106.80  
  Purchase #3 $162.63   6.871%   $173.8043   $173.80   $173.80   $173.80  
  Purchase #4 $232.79   9.336%   $254.5233   $254.52   $254.50   $254.50  
  Purchase #5 $153.51   5.628%   $162.1495   $162.15   $162.15   $162.10  
  Purchase #6 $65.54   13.127%   $74.1434   $74.14   $74.15   $74.10  
  Purchase #7 $59.73   8.754%   $64.9588   $64.96   $64.95   $65.00  
  7 purchase totals = $975.41       $1,060.4422   $1,060.43   $1,060.45   $1,060.30