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 $82.62   8.432%   $89.5865   $89.59   $89.60   $89.60  
  Purchase #2 $127.70   4.306%   $133.1988   $133.20   $133.20   $133.20  
  Purchase #3 $150.39   6.120%   $159.5939   $159.59   $159.60   $159.60  
  Purchase #4 $91.30   8.374%   $98.9455   $98.95   $98.95   $98.90  
  Purchase #5 $236.36   6.628%   $252.0259   $252.03   $252.05   $252.00  
  Purchase #6 $58.60   11.690%   $65.4503   $65.45   $65.45   $65.50  
  Purchase #7 $191.37   11.228%   $212.857   $212.86   $212.85   $212.90  
  7 purchase totals = $938.34       $1,011.6579   $1,011.67   $1,011.70   $1,011.70