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 $216.41   10.621%   $239.3949   $239.39   $239.40   $239.40  
  Purchase #2 $37.31   5.366%   $39.3121   $39.31   $39.30   $39.30  
  Purchase #3 $114.52   9.273%   $125.1394   $125.14   $125.15   $125.10  
  Purchase #4 $207.41   4.592%   $216.9343   $216.93   $216.95   $216.90  
  Purchase #5 $215.89   4.158%   $224.8667   $224.87   $224.85   $224.90  
  Purchase #6 $33.56   9.180%   $36.6408   $36.64   $36.65   $36.60  
  Purchase #7 $194.73   10.279%   $214.7463   $214.75   $214.75   $214.70  
  7 purchase totals = $1,019.83       $1,097.0345   $1,097.03   $1,097.05   $1,096.90