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 $23.93   7.510%   $25.7271   $25.73   $25.75   $25.70  
  Purchase #2 $167.98   5.742%   $177.6254   $177.63   $177.65   $177.60  
  Purchase #3 $39.47   11.649%   $44.0679   $44.07   $44.05   $44.10  
  Purchase #4 $102.40   6.197%   $108.7457   $108.75   $108.75   $108.70  
  Purchase #5 $129.53   6.589%   $138.0647   $138.06   $138.05   $138.10  
  Purchase #6 $190.29   9.808%   $208.9536   $208.95   $208.95   $209.00  
  Purchase #7 $248.93   6.265%   $264.5255   $264.53   $264.55   $264.50  
  7 purchase totals = $902.53       $967.7099   $967.72   $967.75   $967.70