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 $81.70   3.377%   $84.459   $84.46   $84.45   $84.50  
  Purchase #2 $245.72   12.471%   $276.3637   $276.36   $276.35   $276.40  
  Purchase #3 $65.95   9.205%   $72.0207   $72.02   $72.00   $72.00  
  Purchase #4 $103.73   9.539%   $113.6248   $113.62   $113.60   $113.60  
  Purchase #5 $92.98   3.854%   $96.5634   $96.56   $96.55   $96.60  
  Purchase #6 $154.57   12.186%   $173.4059   $173.41   $173.40   $173.40  
  Purchase #7 $223.62   3.258%   $230.9055   $230.91   $230.90   $230.90  
  7 purchase totals = $968.27       $1,047.3430   $1,047.34   $1,047.25   $1,047.40