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 $247.75   3.574%   $256.6046   $256.60   $256.60   $256.60  
  Purchase #2 $49.38   5.456%   $52.0742   $52.07   $52.05   $52.10  
  Purchase #3 $167.46   4.308%   $174.6742   $174.67   $174.65   $174.70  
  Purchase #4 $85.27   11.408%   $94.9976   $95.00   $95.00   $95.00  
  Purchase #5 $197.76   10.558%   $218.6395   $218.64   $218.65   $218.60  
  Purchase #6 $213.43   3.708%   $221.344   $221.34   $221.35   $221.30  
  Purchase #7 $26.65   8.733%   $28.9773   $28.98   $29.00   $29.00  
  7 purchase totals = $987.70       $1,047.3114   $1,047.30   $1,047.30   $1,047.30