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 $34.77   6.257%   $36.9456   $36.95   $36.95   $36.90  
  Purchase #2 $194.37   4.158%   $202.4519   $202.45   $202.45   $202.50  
  Purchase #3 $132.34   8.505%   $143.5955   $143.60   $143.60   $143.60  
  Purchase #4 $244.81   9.858%   $268.9434   $268.94   $268.95   $268.90  
  Purchase #5 $107.80   4.801%   $112.9755   $112.98   $113.00   $113.00  
  Purchase #6 $198.44   11.612%   $221.4829   $221.48   $221.50   $221.50  
  Purchase #7 $28.29   3.408%   $29.2541   $29.25   $29.25   $29.30  
  7 purchase totals = $940.82       $1,015.6489   $1,015.65   $1,015.70   $1,015.70