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 $187.34   3.617%   $194.1161   $194.12   $194.10   $194.10  
  Purchase #2 $198.63   10.593%   $219.6709   $219.67   $219.65   $219.70  
  Purchase #3 $158.31   3.193%   $163.3648   $163.36   $163.35   $163.40  
  Purchase #4 $105.60   8.532%   $114.6098   $114.61   $114.60   $114.60  
  Purchase #5 $162.28   12.232%   $182.1301   $182.13   $182.15   $182.10  
  Purchase #6 $190.52   12.605%   $214.535   $214.54   $214.55   $214.50  
  Purchase #7 $154.94   4.607%   $162.0781   $162.08   $162.10   $162.10  
  7 purchase totals = $1,157.62       $1,250.5048   $1,250.51   $1,250.50   $1,250.50