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 $88.63   9.124%   $96.7166   $96.72   $96.70   $96.70  
  Purchase #2 $43.25   13.167%   $48.9447   $48.94   $48.95   $48.90  
  Purchase #3 $110.96   6.316%   $117.9682   $117.97   $117.95   $118.00  
  Purchase #4 $35.43   11.365%   $39.4566   $39.46   $39.45   $39.50  
  Purchase #5 $44.62   6.379%   $47.4663   $47.47   $47.45   $47.50  
  Purchase #6 $22.60   13.719%   $25.7005   $25.70   $25.70   $25.70  
  Purchase #7 $207.69   12.704%   $234.0749   $234.07   $234.05   $234.10  
  7 purchase totals = $553.18       $610.3278   $610.33   $610.25   $610.40