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 $23.88   8.565%   $25.9253   $25.93   $25.95   $25.90  
  Purchase #2 $216.50   9.228%   $236.4786   $236.48   $236.50   $236.50  
  Purchase #3 $249.55   13.601%   $283.4913   $283.49   $283.50   $283.50  
  Purchase #4 $80.97   6.165%   $85.9618   $85.96   $85.95   $86.00  
  Purchase #5 $107.85   12.463%   $121.2913   $121.29   $121.30   $121.30  
  Purchase #6 $100.75   5.285%   $106.0746   $106.07   $106.05   $106.10  
  Purchase #7 $178.59   4.508%   $186.6408   $186.64   $186.65   $186.60  
  7 purchase totals = $958.09       $1,045.8637   $1,045.86   $1,045.90   $1,045.90