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 $92.76   4.840%   $97.2496   $97.25   $97.25   $97.20  
  Purchase #2 $96.43   6.673%   $102.8648   $102.86   $102.85   $102.90  
  Purchase #3 $242.96   5.570%   $256.4929   $256.49   $256.50   $256.50  
  Purchase #4 $190.30   7.475%   $204.5249   $204.52   $204.50   $204.50  
  Purchase #5 $27.45   6.771%   $29.3086   $29.31   $29.30   $29.30  
  Purchase #6 $26.40   9.810%   $28.9898   $28.99   $29.00   $29.00  
  Purchase #7 $199.26   7.689%   $214.5811   $214.58   $214.60   $214.60  
  7 purchase totals = $875.56       $934.0117   $934.00   $934.00   $934.00