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 $180.37   9.416%   $197.3536   $197.35   $197.35   $197.40  
  Purchase #2 $232.63   3.798%   $241.4653   $241.47   $241.45   $241.50  
  Purchase #3 $69.60   7.151%   $74.5771   $74.58   $74.60   $74.60  
  Purchase #4 $145.90   10.629%   $161.4077   $161.41   $161.40   $161.40  
  Purchase #5 $220.48   9.407%   $241.2206   $241.22   $241.20   $241.20  
  Purchase #6 $88.27   4.600%   $92.3304   $92.33   $92.35   $92.30  
  Purchase #7 $218.32   12.746%   $246.1471   $246.15   $246.15   $246.10  
  7 purchase totals = $1,155.57       $1,254.5018   $1,254.51   $1,254.50   $1,254.50