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 $179.42   13.713%   $204.0239   $204.02   $204.00   $204.00  
  Purchase #2 $16.58   13.344%   $18.7924   $18.79   $18.80   $18.80  
  Purchase #3 $41.88   6.307%   $44.5214   $44.52   $44.50   $44.50  
  Purchase #4 $66.29   9.102%   $72.3237   $72.32   $72.30   $72.30  
  Purchase #5 $19.72   5.866%   $20.8768   $20.88   $20.90   $20.90  
  Purchase #6 $243.48   12.255%   $273.3185   $273.32   $273.30   $273.30  
  Purchase #7 $225.89   12.744%   $254.6774   $254.68   $254.70   $254.70  
  7 purchase totals = $793.26       $888.5341   $888.53   $888.50   $888.50