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 $92.94   5.624%   $98.1669   $98.17   $98.15   $98.20  
  Purchase #2 $61.88   12.485%   $69.6057   $69.61   $69.60   $69.60  
  Purchase #3 $197.88   8.479%   $214.6582   $214.66   $214.65   $214.70  
  Purchase #4 $182.82   12.146%   $205.0253   $205.03   $205.05   $205.00  
  Purchase #5 $11.47   8.264%   $12.4179   $12.42   $12.40   $12.40  
  Purchase #6 $238.25   3.194%   $245.8597   $245.86   $245.85   $245.90  
  Purchase #7 $210.70   7.253%   $225.9821   $225.98   $226.00   $226.00  
  7 purchase totals = $995.94       $1,071.7158   $1,071.73   $1,071.70   $1,071.80