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 $238.38   3.809%   $247.4599   $247.46   $247.45   $247.50  
  Purchase #2 $211.82   4.151%   $220.6126   $220.61   $220.60   $220.60  
  Purchase #3 $247.85   6.815%   $264.741   $264.74   $264.75   $264.70  
  Purchase #4 $59.43   11.551%   $66.2948   $66.29   $66.30   $66.30  
  Purchase #5 $43.48   10.493%   $48.0424   $48.04   $48.05   $48.00  
  Purchase #6 $234.68   8.466%   $254.548   $254.55   $254.55   $254.50  
  Purchase #7 $127.77   3.288%   $131.9711   $131.97   $131.95   $132.00  
  7 purchase totals = $1,163.41       $1,233.6698   $1,233.66   $1,233.65   $1,233.60