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 $241.84   10.185%   $266.4714   $266.47   $266.45   $266.50  
  Purchase #2 $56.99   5.108%   $59.901   $59.90   $59.90   $59.90  
  Purchase #3 $88.60   4.163%   $92.2884   $92.29   $92.30   $92.30  
  Purchase #4 $132.89   5.507%   $140.2083   $140.21   $140.20   $140.20  
  Purchase #5 $197.88   3.574%   $204.9522   $204.95   $204.95   $205.00  
  Purchase #6 $232.70   8.424%   $252.3026   $252.30   $252.30   $252.30  
  Purchase #7 $179.68   3.587%   $186.1251   $186.13   $186.15   $186.10  
  7 purchase totals = $1,130.58       $1,202.2490   $1,202.25   $1,202.25   $1,202.30