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 $75.80   12.439%   $85.2288   $85.23   $85.25   $85.20  
  Purchase #2 $10.40   5.445%   $10.9663   $10.97   $10.95   $11.00  
  Purchase #3 $248.80   8.725%   $270.5078   $270.51   $270.50   $270.50  
  Purchase #4 $173.34   9.144%   $189.1902   $189.19   $189.20   $189.20  
  Purchase #5 $52.48   9.300%   $57.3606   $57.36   $57.35   $57.40  
  Purchase #6 $239.49   11.677%   $267.4552   $267.46   $267.45   $267.50  
  Purchase #7 $194.71   5.605%   $205.6235   $205.62   $205.60   $205.60  
  7 purchase totals = $995.02       $1,086.3324   $1,086.34   $1,086.30   $1,086.40