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 $238.98   8.756%   $259.9051   $259.91   $259.90   $259.90  
  Purchase #2 $210.96   11.717%   $235.6782   $235.68   $235.70   $235.70  
  Purchase #3 $192.50   5.396%   $202.8873   $202.89   $202.90   $202.90  
  Purchase #4 $99.84   9.620%   $109.4446   $109.44   $109.45   $109.40  
  Purchase #5 $16.66   13.548%   $18.9171   $18.92   $18.90   $18.90  
  Purchase #6 $212.52   5.637%   $224.4998   $224.50   $224.50   $224.50  
  Purchase #7 $199.77   8.305%   $216.3609   $216.36   $216.35   $216.40  
  7 purchase totals = $1,171.23       $1,267.6930   $1,267.70   $1,267.70   $1,267.70