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 $153.87   13.293%   $174.3239   $174.32   $174.30   $174.30  
  Purchase #2 $23.38   13.656%   $26.5728   $26.57   $26.55   $26.60  
  Purchase #3 $149.54   9.213%   $163.3171   $163.32   $163.30   $163.30  
  Purchase #4 $66.31   6.189%   $70.4139   $70.41   $70.40   $70.40  
  Purchase #5 $85.81   9.573%   $94.0246   $94.02   $94.00   $94.00  
  Purchase #6 $100.84   4.365%   $105.2417   $105.24   $105.25   $105.20  
  Purchase #7 $106.25   11.510%   $118.4794   $118.48   $118.50   $118.50  
  7 purchase totals = $686.00       $752.3734   $752.36   $752.30   $752.30