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 $218.39   13.343%   $247.5298   $247.53   $247.55   $247.50  
  Purchase #2 $224.41   7.255%   $240.6909   $240.69   $240.70   $240.70  
  Purchase #3 $75.31   12.769%   $84.9263   $84.93   $84.95   $84.90  
  Purchase #4 $121.65   3.182%   $125.5209   $125.52   $125.50   $125.50  
  Purchase #5 $152.80   6.361%   $162.5196   $162.52   $162.50   $162.50  
  Purchase #6 $97.68   6.250%   $103.785   $103.79   $103.80   $103.80  
  Purchase #7 $74.42   10.800%   $82.4574   $82.46   $82.45   $82.50  
  7 purchase totals = $964.66       $1,047.4299   $1,047.44   $1,047.45   $1,047.40