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 $237.60   12.873%   $268.1862   $268.19   $268.20   $268.20  
  Purchase #2 $134.74   6.308%   $143.2394   $143.24   $143.25   $143.20  
  Purchase #3 $241.87   5.261%   $254.5948   $254.59   $254.60   $254.60  
  Purchase #4 $172.98   13.375%   $196.1161   $196.12   $196.10   $196.10  
  Purchase #5 $152.59   6.305%   $162.2108   $162.21   $162.20   $162.20  
  Purchase #6 $248.35   10.277%   $273.8729   $273.87   $273.85   $273.90  
  Purchase #7 $225.83   5.700%   $238.7023   $238.70   $238.70   $238.70  
  7 purchase totals = $1,413.96       $1,536.9225   $1,536.92   $1,536.90   $1,536.90