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 $249.66   13.197%   $282.6076   $282.61   $282.60   $282.60  
  Purchase #2 $201.92   5.226%   $212.4723   $212.47   $212.45   $212.50  
  Purchase #3 $112.88   6.314%   $120.0072   $120.01   $120.00   $120.00  
  Purchase #4 $172.96   5.537%   $182.5368   $182.54   $182.55   $182.50  
  Purchase #5 $171.33   4.464%   $178.9782   $178.98   $179.00   $179.00  
  Purchase #6 $153.74   8.335%   $166.5542   $166.55   $166.55   $166.60  
  Purchase #7 $226.33   5.768%   $239.3847   $239.38   $239.40   $239.40  
  7 purchase totals = $1,288.82       $1,382.5410   $1,382.54   $1,382.55   $1,382.60