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 $92.53   4.808%   $96.9788   $96.98   $97.00   $97.00  
  Purchase #2 $23.52   13.309%   $26.6503   $26.65   $26.65   $26.70  
  Purchase #3 $87.94   5.572%   $92.84   $92.84   $92.85   $92.80  
  Purchase #4 $16.47   10.797%   $18.2483   $18.25   $18.25   $18.20  
  Purchase #5 $131.51   13.535%   $149.3099   $149.31   $149.30   $149.30  
  Purchase #6 $18.88   8.859%   $20.5526   $20.55   $20.55   $20.60  
  Purchase #7 $141.52   10.714%   $156.6825   $156.68   $156.70   $156.70  
  7 purchase totals = $512.37       $561.2624   $561.26   $561.30   $561.30