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 $161.43   11.799%   $180.4771   $180.48   $180.50   $180.50  
  Purchase #2 $214.67   8.382%   $232.6636   $232.66   $232.65   $232.70  
  Purchase #3 $118.57   11.791%   $132.5506   $132.55   $132.55   $132.60  
  Purchase #4 $26.37   3.295%   $27.2389   $27.24   $27.25   $27.20  
  Purchase #5 $205.94   8.321%   $223.0763   $223.08   $223.10   $223.10  
  Purchase #6 $179.57   13.485%   $203.785   $203.79   $203.80   $203.80  
  Purchase #7 $76.99   4.516%   $80.4669   $80.47   $80.45   $80.50  
  7 purchase totals = $983.54       $1,080.2584   $1,080.27   $1,080.30   $1,080.40