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 $221.95   8.694%   $241.2463   $241.25   $241.25   $241.20  
  Purchase #2 $100.36   10.343%   $110.7402   $110.74   $110.75   $110.70  
  Purchase #3 $168.84   6.704%   $180.159   $180.16   $180.15   $180.20  
  Purchase #4 $128.31   3.619%   $132.9535   $132.95   $132.95   $133.00  
  Purchase #5 $33.62   8.565%   $36.4996   $36.50   $36.50   $36.50  
  Purchase #6 $159.80   10.763%   $176.9993   $177.00   $177.00   $177.00  
  Purchase #7 $150.31   4.588%   $157.2062   $157.21   $157.20   $157.20  
  7 purchase totals = $963.19       $1,035.8041   $1,035.81   $1,035.80   $1,035.80