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 $70.67   10.341%   $77.978   $77.98   $78.00   $78.00  
  Purchase #2 $115.36   7.214%   $123.6821   $123.68   $123.70   $123.70  
  Purchase #3 $33.62   4.545%   $35.148   $35.15   $35.15   $35.10  
  Purchase #4 $179.88   6.166%   $190.9714   $190.97   $190.95   $191.00  
  Purchase #5 $201.65   5.769%   $213.2832   $213.28   $213.30   $213.30  
  Purchase #6 $29.31   13.502%   $33.2674   $33.27   $33.25   $33.30  
  Purchase #7 $227.38   11.523%   $253.581   $253.58   $253.60   $253.60  
  7 purchase totals = $857.87       $927.9111   $927.91   $927.95   $928.00