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 $89.61   7.236%   $96.0942   $96.09   $96.10   $96.10  
  Purchase #2 $202.63   9.531%   $221.9427   $221.94   $221.95   $221.90  
  Purchase #3 $74.98   12.800%   $84.5774   $84.58   $84.60   $84.60  
  Purchase #4 $214.47   13.254%   $242.8959   $242.90   $242.90   $242.90  
  Purchase #5 $93.36   9.322%   $102.063   $102.06   $102.05   $102.10  
  Purchase #6 $32.79   3.373%   $33.896   $33.90   $33.90   $33.90  
  Purchase #7 $165.59   5.282%   $174.3365   $174.34   $174.35   $174.30  
  7 purchase totals = $873.43       $955.8057   $955.81   $955.85   $955.80