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 $216.58   11.262%   $240.9712   $240.97   $240.95   $241.00  
  Purchase #2 $91.97   3.662%   $95.3379   $95.34   $95.35   $95.30  
  Purchase #3 $5.54   4.102%   $5.7673   $5.77   $5.75   $5.80  
  Purchase #4 $203.33   11.624%   $226.9651   $226.97   $226.95   $227.00  
  Purchase #5 $191.63   6.480%   $204.0476   $204.05   $204.05   $204.00  
  Purchase #6 $163.55   5.812%   $173.0555   $173.06   $173.05   $173.10  
  Purchase #7 $123.45   10.766%   $136.7406   $136.74   $136.75   $136.70  
  7 purchase totals = $996.05       $1,082.8852   $1,082.90   $1,082.85   $1,082.90