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 $58.88   6.494%   $62.7037   $62.70   $62.70   $62.70  
  Purchase #2 $86.61   7.438%   $93.0521   $93.05   $93.05   $93.10  
  Purchase #3 $63.63   11.618%   $71.0225   $71.02   $71.00   $71.00  
  Purchase #4 $16.41   10.154%   $18.0763   $18.08   $18.10   $18.10  
  Purchase #5 $214.54   7.863%   $231.4093   $231.41   $231.40   $231.40  
  Purchase #6 $244.90   13.289%   $277.4448   $277.44   $277.45   $277.40  
  Purchase #7 $214.34   13.773%   $243.861   $243.86   $243.85   $243.90  
  7 purchase totals = $899.31       $997.5697   $997.56   $997.55   $997.60