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 $218.74   10.303%   $241.2768   $241.28   $241.30   $241.30  
  Purchase #2 $54.84   13.155%   $62.0542   $62.05   $62.05   $62.10  
  Purchase #3 $106.34   10.227%   $117.2154   $117.22   $117.20   $117.20  
  Purchase #4 $96.67   5.740%   $102.2189   $102.22   $102.20   $102.20  
  Purchase #5 $89.69   13.873%   $102.1327   $102.13   $102.15   $102.10  
  Purchase #6 $116.77   12.178%   $130.9903   $130.99   $131.00   $131.00  
  Purchase #7 $94.99   8.800%   $103.3491   $103.35   $103.35   $103.30  
  7 purchase totals = $778.04       $859.2374   $859.24   $859.25   $859.20