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 $59.34   11.716%   $66.2923   $66.29   $66.30   $66.30  
  Purchase #2 $236.53   10.477%   $261.3112   $261.31   $261.30   $261.30  
  Purchase #3 $241.42   6.866%   $257.9959   $258.00   $258.00   $258.00  
  Purchase #4 $179.52   9.771%   $197.0609   $197.06   $197.05   $197.10  
  Purchase #5 $191.46   8.395%   $207.5331   $207.53   $207.55   $207.50  
  Purchase #6 $68.98   4.190%   $71.8703   $71.87   $71.85   $71.90  
  Purchase #7 $110.50   12.616%   $124.4407   $124.44   $124.45   $124.40  
  7 purchase totals = $1,087.75       $1,186.5044   $1,186.50   $1,186.50   $1,186.50