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 $95.63   9.397%   $104.6164   $104.62   $104.60   $104.60  
  Purchase #2 $244.52   11.566%   $272.8012   $272.80   $272.80   $272.80  
  Purchase #3 $59.61   6.751%   $63.6343   $63.63   $63.65   $63.60  
  Purchase #4 $30.34   4.678%   $31.7593   $31.76   $31.75   $31.80  
  Purchase #5 $101.45   5.668%   $107.2002   $107.20   $107.20   $107.20  
  Purchase #6 $141.76   9.330%   $154.9862   $154.99   $155.00   $155.00  
  Purchase #7 $233.38   3.241%   $240.9438   $240.94   $240.95   $240.90  
  7 purchase totals = $906.69       $975.9414   $975.94   $975.95   $975.90