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 $70.34   6.601%   $74.9831   $74.98   $75.00   $75.00  
  Purchase #2 $209.37   13.164%   $236.9315   $236.93   $236.95   $236.90  
  Purchase #3 $238.74   9.724%   $261.9551   $261.96   $261.95   $262.00  
  Purchase #4 $156.32   11.407%   $174.1514   $174.15   $174.15   $174.20  
  Purchase #5 $126.76   6.679%   $135.2263   $135.23   $135.25   $135.20  
  Purchase #6 $239.59   10.542%   $264.8476   $264.85   $264.85   $264.80  
  Purchase #7 $186.47   7.519%   $200.4907   $200.49   $200.50   $200.50  
  7 purchase totals = $1,227.59       $1,348.5857   $1,348.59   $1,348.65   $1,348.60