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 $82.49   6.240%   $87.6374   $87.64   $87.65   $87.60  
  Purchase #2 $123.66   10.587%   $136.7519   $136.75   $136.75   $136.80  
  Purchase #3 $52.50   13.615%   $59.6479   $59.65   $59.65   $59.60  
  Purchase #4 $106.98   12.862%   $120.7398   $120.74   $120.75   $120.70  
  Purchase #5 $26.70   13.482%   $30.2997   $30.30   $30.30   $30.30  
  Purchase #6 $176.65   13.667%   $200.7928   $200.79   $200.80   $200.80  
  Purchase #7 $249.36   6.351%   $265.1969   $265.20   $265.20   $265.20  
  7 purchase totals = $818.34       $901.0664   $901.07   $901.10   $901.00