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 $100.80   4.525%   $105.3612   $105.36   $105.35   $105.40  
  Purchase #2 $108.33   7.445%   $116.3952   $116.40   $116.40   $116.40  
  Purchase #3 $74.49   11.603%   $83.1331   $83.13   $83.15   $83.10  
  Purchase #4 $249.74   13.191%   $282.6832   $282.68   $282.70   $282.70  
  Purchase #5 $169.85   6.427%   $180.7663   $180.77   $180.75   $180.80  
  Purchase #6 $190.44   6.541%   $202.8967   $202.90   $202.90   $202.90  
  Purchase #7 $23.54   5.591%   $24.8561   $24.86   $24.85   $24.90  
  7 purchase totals = $917.19       $996.0918   $996.10   $996.10   $996.20