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 $233.38   8.424%   $253.0399   $253.04   $253.05   $253.00  
  Purchase #2 $208.98   5.428%   $220.3234   $220.32   $220.30   $220.30  
  Purchase #3 $246.90   12.861%   $278.6538   $278.65   $278.65   $278.70  
  Purchase #4 $16.81   10.802%   $18.6258   $18.63   $18.65   $18.60  
  Purchase #5 $122.36   9.250%   $133.6783   $133.68   $133.70   $133.70  
  Purchase #6 $25.71   6.543%   $27.3922   $27.39   $27.40   $27.40  
  Purchase #7 $219.44   4.440%   $229.1831   $229.18   $229.20   $229.20  
  7 purchase totals = $1,073.58       $1,160.8965   $1,160.89   $1,160.95   $1,160.90