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 $140.59   10.217%   $154.9541   $154.95   $154.95   $155.00  
  Purchase #2 $93.95   7.486%   $100.9831   $100.98   $101.00   $101.00  
  Purchase #3 $100.67   10.237%   $110.9756   $110.98   $111.00   $111.00  
  Purchase #4 $165.72   3.351%   $171.2733   $171.27   $171.25   $171.30  
  Purchase #5 $174.94   3.351%   $180.8022   $180.80   $180.80   $180.80  
  Purchase #6 $193.55   9.177%   $211.3121   $211.31   $211.30   $211.30  
  Purchase #7 $35.73   4.268%   $37.255   $37.26   $37.25   $37.30  
  7 purchase totals = $905.15       $967.5554   $967.55   $967.55   $967.70