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 $57.65   10.269%   $63.5701   $63.57   $63.55   $63.60  
  Purchase #2 $246.69   13.723%   $280.5433   $280.54   $280.55   $280.50  
  Purchase #3 $83.55   9.177%   $91.2174   $91.22   $91.20   $91.20  
  Purchase #4 $205.61   4.405%   $214.6671   $214.67   $214.65   $214.70  
  Purchase #5 $57.51   5.428%   $60.6316   $60.63   $60.65   $60.60  
  Purchase #6 $132.51   11.438%   $147.6665   $147.67   $147.65   $147.70  
  Purchase #7 $156.68   7.385%   $168.2508   $168.25   $168.25   $168.30  
  7 purchase totals = $940.20       $1,026.5468   $1,026.55   $1,026.50   $1,026.60