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 $169.97   10.437%   $187.7098   $187.71   $187.70   $187.70  
  Purchase #2 $152.54   3.333%   $157.6242   $157.62   $157.60   $157.60  
  Purchase #3 $27.96   3.452%   $28.9252   $28.93   $28.95   $28.90  
  Purchase #4 $227.72   11.518%   $253.9488   $253.95   $253.95   $253.90  
  Purchase #5 $90.80   8.850%   $98.8358   $98.84   $98.85   $98.80  
  Purchase #6 $40.25   4.195%   $41.9385   $41.94   $41.95   $41.90  
  Purchase #7 $244.59   3.133%   $252.253   $252.25   $252.25   $252.30  
  7 purchase totals = $953.83       $1,021.2353   $1,021.24   $1,021.25   $1,021.10