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 $54.50   8.535%   $59.1516   $59.15   $59.15   $59.20  
  Purchase #2 $160.33   10.165%   $176.6275   $176.63   $176.65   $176.60  
  Purchase #3 $243.72   6.578%   $259.7519   $259.75   $259.75   $259.80  
  Purchase #4 $143.97   12.253%   $161.6106   $161.61   $161.60   $161.60  
  Purchase #5 $145.37   12.751%   $163.9061   $163.91   $163.90   $163.90  
  Purchase #6 $184.27   6.296%   $195.8716   $195.87   $195.85   $195.90  
  Purchase #7 $201.73   12.695%   $227.3396   $227.34   $227.35   $227.30  
  7 purchase totals = $1,133.89       $1,244.2589   $1,244.26   $1,244.25   $1,244.30