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 $83.56   13.486%   $94.8289   $94.83   $94.85   $94.80  
  Purchase #2 $7.29   7.862%   $7.8631   $7.86   $7.85   $7.90  
  Purchase #3 $54.84   7.737%   $59.083   $59.08   $59.10   $59.10  
  Purchase #4 $224.77   7.239%   $241.0411   $241.04   $241.05   $241.00  
  Purchase #5 $56.68   3.552%   $58.6933   $58.69   $58.70   $58.70  
  Purchase #6 $141.98   12.327%   $159.4819   $159.48   $159.50   $159.50  
  Purchase #7 $233.91   5.647%   $247.1189   $247.12   $247.10   $247.10  
  7 purchase totals = $803.03       $868.1102   $868.10   $868.15   $868.10