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 $38.47   11.869%   $43.036   $43.04   $43.05   $43.00  
  Purchase #2 $235.59   12.187%   $264.3014   $264.30   $264.30   $264.30  
  Purchase #3 $104.82   4.789%   $109.8398   $109.84   $109.85   $109.80  
  Purchase #4 $222.60   8.472%   $241.4587   $241.46   $241.45   $241.50  
  Purchase #5 $67.70   11.115%   $75.2249   $75.22   $75.20   $75.20  
  Purchase #6 $35.41   11.346%   $39.4276   $39.43   $39.45   $39.40  
  Purchase #7 $133.38   9.614%   $146.2032   $146.20   $146.20   $146.20  
  7 purchase totals = $837.97       $919.4916   $919.49   $919.50   $919.40