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 $44.69   13.115%   $50.5511   $50.55   $50.55   $50.60  
  Purchase #2 $97.43   9.344%   $106.5339   $106.53   $106.55   $106.50  
  Purchase #3 $194.43   13.307%   $220.3028   $220.30   $220.30   $220.30  
  Purchase #4 $51.74   11.279%   $57.5758   $57.58   $57.60   $57.60  
  Purchase #5 $175.32   10.802%   $194.2581   $194.26   $194.25   $194.30  
  Purchase #6 $122.35   11.235%   $136.096   $136.10   $136.10   $136.10  
  Purchase #7 $165.28   12.205%   $185.4524   $185.45   $185.45   $185.50  
  7 purchase totals = $851.24       $950.7701   $950.77   $950.80   $950.90