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 $154.67   13.617%   $175.7314   $175.73   $175.75   $175.70  
  Purchase #2 $41.72   11.596%   $46.5579   $46.56   $46.55   $46.60  
  Purchase #3 $116.57   7.582%   $125.4083   $125.41   $125.40   $125.40  
  Purchase #4 $142.46   10.526%   $157.4553   $157.46   $157.45   $157.50  
  Purchase #5 $150.30   11.502%   $167.5875   $167.59   $167.60   $167.60  
  Purchase #6 $224.48   10.398%   $247.8214   $247.82   $247.80   $247.80  
  Purchase #7 $95.47   5.787%   $100.9948   $100.99   $101.00   $101.00  
  7 purchase totals = $925.67       $1,021.5566   $1,021.56   $1,021.55   $1,021.60