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 $97.66   12.829%   $110.1888   $110.19   $110.20   $110.20  
  Purchase #2 $162.26   5.367%   $170.9685   $170.97   $170.95   $171.00  
  Purchase #3 $199.25   3.379%   $205.9827   $205.98   $206.00   $206.00  
  Purchase #4 $27.99   5.721%   $29.5913   $29.59   $29.60   $29.60  
  Purchase #5 $211.90   10.294%   $233.713   $233.71   $233.70   $233.70  
  Purchase #6 $45.91   9.475%   $50.26   $50.26   $50.25   $50.30  
  Purchase #7 $179.62   8.804%   $195.4337   $195.43   $195.45   $195.40  
  7 purchase totals = $924.59       $996.1380   $996.13   $996.15   $996.20