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 $84.54   10.337%   $93.2789   $93.28   $93.30   $93.30  
  Purchase #2 $113.87   4.204%   $118.6571   $118.66   $118.65   $118.70  
  Purchase #3 $94.26   4.126%   $98.1492   $98.15   $98.15   $98.10  
  Purchase #4 $162.26   11.872%   $181.5235   $181.52   $181.50   $181.50  
  Purchase #5 $125.97   13.378%   $142.8223   $142.82   $142.80   $142.80  
  Purchase #6 $93.60   13.751%   $106.4709   $106.47   $106.45   $106.50  
  Purchase #7 $61.42   8.397%   $66.5774   $66.58   $66.60   $66.60  
  7 purchase totals = $735.92       $807.4793   $807.48   $807.45   $807.50