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 $235.98   9.232%   $257.7657   $257.77   $257.75   $257.80  
  Purchase #2 $161.26   7.134%   $172.7643   $172.76   $172.75   $172.80  
  Purchase #3 $176.46   9.192%   $192.6802   $192.68   $192.70   $192.70  
  Purchase #4 $203.27   11.180%   $225.9956   $226.00   $226.00   $226.00  
  Purchase #5 $193.65   11.125%   $215.1936   $215.19   $215.20   $215.20  
  Purchase #6 $215.51   8.491%   $233.809   $233.81   $233.80   $233.80  
  Purchase #7 $162.48   12.671%   $183.0678   $183.07   $183.05   $183.10  
  7 purchase totals = $1,348.61       $1,481.2762   $1,481.28   $1,481.25   $1,481.40