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 $105.56   13.605%   $119.9214   $119.92   $119.90   $119.90  
  Purchase #2 $153.82   8.464%   $166.8393   $166.84   $166.85   $166.80  
  Purchase #3 $243.34   10.767%   $269.5404   $269.54   $269.55   $269.50  
  Purchase #4 $215.54   10.121%   $237.3548   $237.35   $237.35   $237.40  
  Purchase #5 $192.63   13.211%   $218.0783   $218.08   $218.10   $218.10  
  Purchase #6 $200.47   3.730%   $207.9475   $207.95   $207.95   $207.90  
  Purchase #7 $217.91   6.555%   $232.194   $232.19   $232.20   $232.20  
  7 purchase totals = $1,329.27       $1,451.8757   $1,451.87   $1,451.90   $1,451.80