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 $61.46   8.459%   $66.6589   $66.66   $66.65   $66.70  
  Purchase #2 $64.72   11.559%   $72.201   $72.20   $72.20   $72.20  
  Purchase #3 $77.87   7.281%   $83.5397   $83.54   $83.55   $83.50  
  Purchase #4 $195.57   3.224%   $201.8752   $201.88   $201.90   $201.90  
  Purchase #5 $11.49   8.595%   $12.4776   $12.48   $12.50   $12.50  
  Purchase #6 $48.64   4.121%   $50.6445   $50.64   $50.65   $50.60  
  Purchase #7 $212.96   8.107%   $230.2247   $230.22   $230.20   $230.20  
  7 purchase totals = $672.71       $717.6216   $717.62   $717.65   $717.60