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 $59.33   11.756%   $66.3048   $66.30   $66.30   $66.30  
  Purchase #2 $208.79   12.411%   $234.7029   $234.70   $234.70   $234.70  
  Purchase #3 $139.55   4.309%   $145.5632   $145.56   $145.55   $145.60  
  Purchase #4 $164.68   7.555%   $177.1216   $177.12   $177.10   $177.10  
  Purchase #5 $152.28   11.860%   $170.3404   $170.34   $170.35   $170.30  
  Purchase #6 $70.86   8.486%   $76.8732   $76.87   $76.85   $76.90  
  Purchase #7 $54.64   7.514%   $58.7456   $58.75   $58.75   $58.70  
  7 purchase totals = $850.13       $929.6517   $929.64   $929.60   $929.60