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 $134.88   12.621%   $151.9032   $151.90   $151.90   $151.90  
  Purchase #2 $243.32   9.849%   $267.2846   $267.28   $267.30   $267.30  
  Purchase #3 $177.49   4.139%   $184.8363   $184.84   $184.85   $184.80  
  Purchase #4 $242.68   6.179%   $257.6752   $257.68   $257.70   $257.70  
  Purchase #5 $191.80   8.380%   $207.8728   $207.87   $207.85   $207.90  
  Purchase #6 $136.86   9.152%   $149.3854   $149.39   $149.40   $149.40  
  Purchase #7 $127.26   5.675%   $134.482   $134.48   $134.50   $134.50  
  7 purchase totals = $1,254.29       $1,353.4395   $1,353.44   $1,353.50   $1,353.50