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 $232.39   12.435%   $261.2877   $261.29   $261.30   $261.30  
  Purchase #2 $168.55   13.693%   $191.6296   $191.63   $191.65   $191.60  
  Purchase #3 $92.31   8.238%   $99.9145   $99.91   $99.90   $99.90  
  Purchase #4 $209.35   12.405%   $235.3199   $235.32   $235.30   $235.30  
  Purchase #5 $135.44   12.163%   $151.9136   $151.91   $151.90   $151.90  
  Purchase #6 $162.74   9.437%   $178.0978   $178.10   $178.10   $178.10  
  Purchase #7 $227.99   11.670%   $254.5964   $254.60   $254.60   $254.60  
  7 purchase totals = $1,228.77       $1,372.7595   $1,372.76   $1,372.75   $1,372.70