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 $92.74   6.128%   $98.4231   $98.42   $98.40   $98.40  
  Purchase #2 $40.92   8.823%   $44.5304   $44.53   $44.55   $44.50  
  Purchase #3 $83.35   7.490%   $89.5929   $89.59   $89.60   $89.60  
  Purchase #4 $206.37   12.797%   $232.7792   $232.78   $232.80   $232.80  
  Purchase #5 $203.51   6.578%   $216.8969   $216.90   $216.90   $216.90  
  Purchase #6 $150.29   5.797%   $159.0023   $159.00   $159.00   $159.00  
  Purchase #7 $17.50   7.189%   $18.7581   $18.76   $18.75   $18.80  
  7 purchase totals = $794.68       $859.9829   $859.98   $860.00   $860.00