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 $233.54   5.732%   $246.9265   $246.93   $246.95   $246.90  
  Purchase #2 $95.46   3.688%   $98.9806   $98.98   $99.00   $99.00  
  Purchase #3 $240.55   7.466%   $258.5095   $258.51   $258.50   $258.50  
  Purchase #4 $97.27   5.128%   $102.258   $102.26   $102.25   $102.30  
  Purchase #5 $147.51   11.610%   $164.6359   $164.64   $164.65   $164.60  
  Purchase #6 $101.79   8.120%   $110.0553   $110.06   $110.05   $110.10  
  Purchase #7 $71.48   5.251%   $75.2334   $75.23   $75.25   $75.20  
  7 purchase totals = $987.60       $1,056.5992   $1,056.61   $1,056.65   $1,056.60