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 $61.68   5.760%   $65.2328   $65.23   $65.25   $65.20  
  Purchase #2 $148.94   7.688%   $160.3905   $160.39   $160.40   $160.40  
  Purchase #3 $113.33   13.667%   $128.8188   $128.82   $128.80   $128.80  
  Purchase #4 $149.80   4.707%   $156.8511   $156.85   $156.85   $156.90  
  Purchase #5 $45.25   12.824%   $51.0529   $51.05   $51.05   $51.10  
  Purchase #6 $14.39   11.419%   $16.0332   $16.03   $16.05   $16.00  
  Purchase #7 $117.60   10.819%   $130.3231   $130.32   $130.30   $130.30  
  7 purchase totals = $650.99       $708.7024   $708.69   $708.70   $708.70