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 $168.99   10.800%   $187.2409   $187.24   $187.25   $187.20  
  Purchase #2 $25.41   9.218%   $27.7523   $27.75   $27.75   $27.80  
  Purchase #3 $181.29   3.137%   $186.9771   $186.98   $187.00   $187.00  
  Purchase #4 $239.77   11.704%   $267.8327   $267.83   $267.85   $267.80  
  Purchase #5 $237.63   6.487%   $253.0451   $253.05   $253.05   $253.00  
  Purchase #6 $105.92   4.817%   $111.0222   $111.02   $111.00   $111.00  
  Purchase #7 $8.74   11.147%   $9.7142   $9.71   $9.70   $9.70  
  7 purchase totals = $967.75       $1,043.5845   $1,043.58   $1,043.60   $1,043.50