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 $158.99   11.142%   $176.7047   $176.70   $176.70   $176.70  
  Purchase #2 $63.36   5.334%   $66.7396   $66.74   $66.75   $66.70  
  Purchase #3 $161.87   5.230%   $170.3358   $170.34   $170.35   $170.30  
  Purchase #4 $66.27   5.316%   $69.7929   $69.79   $69.80   $69.80  
  Purchase #5 $194.93   13.385%   $221.0214   $221.02   $221.00   $221.00  
  Purchase #6 $248.88   4.415%   $259.8681   $259.87   $259.85   $259.90  
  Purchase #7 $53.92   8.294%   $58.3921   $58.39   $58.40   $58.40  
  7 purchase totals = $948.22       $1,022.8546   $1,022.85   $1,022.85   $1,022.80