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 $46.27   8.787%   $50.3357   $50.34   $50.35   $50.30  
  Purchase #2 $211.81   7.103%   $226.8549   $226.85   $226.85   $226.90  
  Purchase #3 $58.35   9.807%   $64.0724   $64.07   $64.05   $64.10  
  Purchase #4 $242.60   8.440%   $263.0754   $263.08   $263.10   $263.10  
  Purchase #5 $119.84   13.712%   $136.2725   $136.27   $136.25   $136.30  
  Purchase #6 $171.89   11.532%   $191.7124   $191.71   $191.70   $191.70  
  Purchase #7 $228.50   5.228%   $240.446   $240.45   $240.45   $240.40  
  7 purchase totals = $1,079.26       $1,172.7693   $1,172.77   $1,172.75   $1,172.80