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 $86.44   13.731%   $98.3091   $98.31   $98.30   $98.30  
  Purchase #2 $159.46   9.697%   $174.9228   $174.92   $174.90   $174.90  
  Purchase #3 $83.79   13.386%   $95.0061   $95.01   $95.00   $95.00  
  Purchase #4 $116.61   12.494%   $131.1793   $131.18   $131.20   $131.20  
  Purchase #5 $148.94   9.409%   $162.9538   $162.95   $162.95   $163.00  
  Purchase #6 $245.53   5.767%   $259.6897   $259.69   $259.70   $259.70  
  Purchase #7 $27.86   12.530%   $31.3509   $31.35   $31.35   $31.40  
  7 purchase totals = $868.63       $953.4117   $953.41   $953.40   $953.50