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 $86.75   11.500%   $96.7263   $96.73   $96.75   $96.70  
  Purchase #2 $200.76   10.584%   $222.0084   $222.01   $222.00   $222.00  
  Purchase #3 $158.78   8.693%   $172.5827   $172.58   $172.60   $172.60  
  Purchase #4 $219.39   7.785%   $236.4695   $236.47   $236.45   $236.50  
  Purchase #5 $208.67   6.844%   $222.9514   $222.95   $222.95   $223.00  
  Purchase #6 $204.59   9.818%   $224.6766   $224.68   $224.70   $224.70  
  Purchase #7 $243.79   9.426%   $266.7696   $266.77   $266.75   $266.80  
  7 purchase totals = $1,322.73       $1,442.1845   $1,442.19   $1,442.20   $1,442.30