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 $134.69   13.414%   $152.7573   $152.76   $152.75   $152.80  
  Purchase #2 $185.74   9.391%   $203.1828   $203.18   $203.20   $203.20  
  Purchase #3 $88.60   3.458%   $91.6638   $91.66   $91.65   $91.70  
  Purchase #4 $197.66   11.730%   $220.8455   $220.85   $220.85   $220.80  
  Purchase #5 $216.45   7.242%   $232.1253   $232.13   $232.15   $232.10  
  Purchase #6 $115.93   6.788%   $123.7993   $123.80   $123.80   $123.80  
  Purchase #7 $164.99   7.213%   $176.8907   $176.89   $176.90   $176.90  
  7 purchase totals = $1,104.06       $1,201.2647   $1,201.27   $1,201.30   $1,201.30