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 $92.92   4.224%   $96.8449   $96.84   $96.85   $96.80  
  Purchase #2 $210.54   7.298%   $225.9052   $225.91   $225.90   $225.90  
  Purchase #3 $34.91   5.786%   $36.9299   $36.93   $36.95   $36.90  
  Purchase #4 $170.28   4.235%   $177.4914   $177.49   $177.50   $177.50  
  Purchase #5 $69.54   12.787%   $78.4321   $78.43   $78.45   $78.40  
  Purchase #6 $169.55   5.596%   $179.038   $179.04   $179.05   $179.00  
  Purchase #7 $208.95   10.358%   $230.593   $230.59   $230.60   $230.60  
  7 purchase totals = $956.69       $1,025.2345   $1,025.23   $1,025.30   $1,025.10