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 $87.29   11.779%   $97.5719   $97.57   $97.55   $97.60  
  Purchase #2 $244.97   9.618%   $268.5312   $268.53   $268.55   $268.50  
  Purchase #3 $154.67   12.582%   $174.1306   $174.13   $174.15   $174.10  
  Purchase #4 $222.73   11.111%   $247.4775   $247.48   $247.50   $247.50  
  Purchase #5 $78.61   10.248%   $86.666   $86.67   $86.65   $86.70  
  Purchase #6 $156.32   6.151%   $165.9352   $165.94   $165.95   $165.90  
  Purchase #7 $223.35   8.699%   $242.7792   $242.78   $242.80   $242.80  
  7 purchase totals = $1,167.94       $1,283.0916   $1,283.10   $1,283.15   $1,283.10