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 $157.93   12.227%   $177.2401   $177.24   $177.25   $177.20  
  Purchase #2 $188.73   11.647%   $210.7114   $210.71   $210.70   $210.70  
  Purchase #3 $154.99   11.111%   $172.2109   $172.21   $172.20   $172.20  
  Purchase #4 $59.64   3.550%   $61.7572   $61.76   $61.75   $61.80  
  Purchase #5 $60.90   12.270%   $68.3724   $68.37   $68.35   $68.40  
  Purchase #6 $162.33   5.568%   $171.3685   $171.37   $171.35   $171.40  
  Purchase #7 $248.47   10.672%   $274.9867   $274.99   $275.00   $275.00  
  7 purchase totals = $1,032.99       $1,136.6472   $1,136.65   $1,136.60   $1,136.70