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 $209.69   6.794%   $223.9363   $223.94   $223.95   $223.90  
  Purchase #2 $83.86   10.253%   $92.4582   $92.46   $92.45   $92.50  
  Purchase #3 $86.30   11.251%   $96.0096   $96.01   $96.00   $96.00  
  Purchase #4 $137.96   9.452%   $151   $151.00   $151.00   $151.00  
  Purchase #5 $249.70   8.568%   $271.0943   $271.09   $271.10   $271.10  
  Purchase #6 $24.46   9.717%   $26.8368   $26.84   $26.85   $26.80  
  Purchase #7 $130.83   6.743%   $139.6519   $139.65   $139.65   $139.70  
  7 purchase totals = $922.80       $1,000.9871   $1,000.99   $1,001.00   $1,001.00