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 $30.95   8.603%   $33.6126   $33.61   $33.60   $33.60  
  Purchase #2 $243.51   11.128%   $270.6078   $270.61   $270.60   $270.60  
  Purchase #3 $21.34   11.686%   $23.8338   $23.83   $23.85   $23.80  
  Purchase #4 $161.93   10.666%   $179.2015   $179.20   $179.20   $179.20  
  Purchase #5 $225.82   12.835%   $254.804   $254.80   $254.80   $254.80  
  Purchase #6 $226.77   12.211%   $254.4609   $254.46   $254.45   $254.50  
  Purchase #7 $83.74   5.227%   $88.1171   $88.12   $88.10   $88.10  
  7 purchase totals = $994.06       $1,104.6377   $1,104.63   $1,104.60   $1,104.60