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 $244.67   8.387%   $265.1905   $265.19   $265.20   $265.20  
  Purchase #2 $244.34   10.138%   $269.1112   $269.11   $269.10   $269.10  
  Purchase #3 $170.60   10.772%   $188.977   $188.98   $189.00   $189.00  
  Purchase #4 $28.53   8.701%   $31.0124   $31.01   $31.00   $31.00  
  Purchase #5 $144.51   4.506%   $151.0216   $151.02   $151.00   $151.00  
  Purchase #6 $170.85   5.690%   $180.5714   $180.57   $180.55   $180.60  
  Purchase #7 $215.38   11.294%   $239.705   $239.71   $239.70   $239.70  
  7 purchase totals = $1,218.88       $1,325.5891   $1,325.59   $1,325.55   $1,325.60