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 $76.67   12.424%   $86.1955   $86.20   $86.20   $86.20  
  Purchase #2 $148.63   6.511%   $158.3073   $158.31   $158.30   $158.30  
  Purchase #3 $133.98   10.120%   $147.5388   $147.54   $147.55   $147.50  
  Purchase #4 $201.84   11.173%   $224.3916   $224.39   $224.40   $224.40  
  Purchase #5 $151.25   6.663%   $161.3278   $161.33   $161.35   $161.30  
  Purchase #6 $236.41   10.530%   $261.304   $261.30   $261.30   $261.30  
  Purchase #7 $192.75   9.821%   $211.68   $211.68   $211.70   $211.70  
  7 purchase totals = $1,141.53       $1,250.7450   $1,250.75   $1,250.80   $1,250.70