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 $127.43   6.780%   $136.0698   $136.07   $136.05   $136.10  
  Purchase #2 $232.48   12.213%   $260.8728   $260.87   $260.85   $260.90  
  Purchase #3 $120.29   6.356%   $127.9356   $127.94   $127.95   $127.90  
  Purchase #4 $89.36   8.275%   $96.7545   $96.75   $96.75   $96.80  
  Purchase #5 $157.29   6.594%   $167.6617   $167.66   $167.65   $167.70  
  Purchase #6 $46.30   9.756%   $50.817   $50.82   $50.80   $50.80  
  Purchase #7 $11.28   13.501%   $12.8029   $12.80   $12.80   $12.80  
  7 purchase totals = $784.43       $852.9143   $852.91   $852.85   $853.00