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 $185.75   8.554%   $201.6391   $201.64   $201.65   $201.60  
  Purchase #2 $13.86   7.627%   $14.9171   $14.92   $14.90   $14.90  
  Purchase #3 $205.49   6.733%   $219.3256   $219.33   $219.35   $219.30  
  Purchase #4 $50.86   7.262%   $54.5535   $54.55   $54.55   $54.60  
  Purchase #5 $47.68   8.668%   $51.8129   $51.81   $51.80   $51.80  
  Purchase #6 $79.61   9.511%   $87.1817   $87.18   $87.20   $87.20  
  Purchase #7 $130.52   6.322%   $138.7715   $138.77   $138.75   $138.80  
  7 purchase totals = $713.77       $768.2014   $768.20   $768.20   $768.20