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 $97.98   8.644%   $106.4494   $106.45   $106.45   $106.40  
  Purchase #2 $176.95   9.256%   $193.3285   $193.33   $193.35   $193.30  
  Purchase #3 $214.94   4.485%   $224.5801   $224.58   $224.60   $224.60  
  Purchase #4 $123.33   9.489%   $135.0328   $135.03   $135.05   $135.00  
  Purchase #5 $232.86   8.860%   $253.4914   $253.49   $253.50   $253.50  
  Purchase #6 $171.67   11.366%   $191.182   $191.18   $191.20   $191.20  
  Purchase #7 $165.89   3.397%   $171.5253   $171.53   $171.55   $171.50  
  7 purchase totals = $1,183.62       $1,275.5895   $1,275.59   $1,275.70   $1,275.50