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 $214.60   12.791%   $242.0495   $242.05   $242.05   $242.00  
  Purchase #2 $85.70   8.695%   $93.1516   $93.15   $93.15   $93.20  
  Purchase #3 $250.47   3.672%   $259.6673   $259.67   $259.65   $259.70  
  Purchase #4 $145.50   12.212%   $163.2685   $163.27   $163.25   $163.30  
  Purchase #5 $150.29   7.572%   $161.67   $161.67   $161.65   $161.70  
  Purchase #6 $40.84   13.299%   $46.2713   $46.27   $46.25   $46.30  
  Purchase #7 $58.42   12.576%   $65.7669   $65.77   $65.75   $65.80  
  7 purchase totals = $945.82       $1,031.8451   $1,031.85   $1,031.75   $1,032.00