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 $241.31   13.179%   $273.1122   $273.11   $273.10   $273.10  
  Purchase #2 $229.29   6.260%   $243.6436   $243.64   $243.65   $243.60  
  Purchase #3 $77.88   6.193%   $82.7031   $82.70   $82.70   $82.70  
  Purchase #4 $23.61   7.783%   $25.4476   $25.45   $25.45   $25.40  
  Purchase #5 $126.47   6.158%   $134.258   $134.26   $134.25   $134.30  
  Purchase #6 $65.42   8.569%   $71.0258   $71.03   $71.05   $71.00  
  Purchase #7 $108.87   13.840%   $123.9376   $123.94   $123.95   $123.90  
  7 purchase totals = $872.85       $954.1279   $954.13   $954.15   $954.00