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 $23.53   5.155%   $24.743   $24.74   $24.75   $24.70  
  Purchase #2 $51.88   13.220%   $58.7385   $58.74   $58.75   $58.70  
  Purchase #3 $215.36   12.555%   $242.3984   $242.40   $242.40   $242.40  
  Purchase #4 $233.34   9.293%   $255.0243   $255.02   $255.00   $255.00  
  Purchase #5 $203.74   4.420%   $212.7453   $212.75   $212.75   $212.70  
  Purchase #6 $119.70   3.241%   $123.5795   $123.58   $123.60   $123.60  
  Purchase #7 $94.61   8.111%   $102.2838   $102.28   $102.30   $102.30  
  7 purchase totals = $942.16       $1,019.5128   $1,019.51   $1,019.55   $1,019.40