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 $28.71   13.682%   $32.6381   $32.64   $32.65   $32.60  
  Purchase #2 $182.28   6.633%   $194.3706   $194.37   $194.35   $194.40  
  Purchase #3 $205.35   9.400%   $224.6529   $224.65   $224.65   $224.70  
  Purchase #4 $141.92   10.826%   $157.2843   $157.28   $157.30   $157.30  
  Purchase #5 $84.84   9.210%   $92.6538   $92.65   $92.65   $92.70  
  Purchase #6 $220.25   8.674%   $239.3545   $239.35   $239.35   $239.40  
  Purchase #7 $80.89   10.513%   $89.394   $89.39   $89.40   $89.40  
  7 purchase totals = $944.24       $1,030.3482   $1,030.33   $1,030.35   $1,030.50