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 $32.47   9.531%   $35.5647   $35.56   $35.55   $35.60  
  Purchase #2 $62.98   7.235%   $67.5366   $67.54   $67.55   $67.50  
  Purchase #3 $24.80   10.310%   $27.3569   $27.36   $27.35   $27.40  
  Purchase #4 $122.96   5.568%   $129.8064   $129.81   $129.80   $129.80  
  Purchase #5 $225.59   7.165%   $241.7535   $241.75   $241.75   $241.80  
  Purchase #6 $189.83   8.299%   $205.584   $205.58   $205.60   $205.60  
  Purchase #7 $102.41   6.692%   $109.2633   $109.26   $109.25   $109.30  
  7 purchase totals = $761.04       $816.8654   $816.86   $816.85   $817.00