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 $49.58   6.856%   $52.9792   $52.98   $53.00   $53.00  
  Purchase #2 $67.38   11.256%   $74.9643   $74.96   $74.95   $75.00  
  Purchase #3 $56.27   5.285%   $59.2439   $59.24   $59.25   $59.20  
  Purchase #4 $89.51   9.305%   $97.8389   $97.84   $97.85   $97.80  
  Purchase #5 $26.89   8.844%   $29.2682   $29.27   $29.25   $29.30  
  Purchase #6 $233.91   12.491%   $263.1277   $263.13   $263.15   $263.10  
  Purchase #7 $125.60   7.657%   $135.2172   $135.22   $135.20   $135.20  
  7 purchase totals = $649.14       $712.6394   $712.64   $712.65   $712.60