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 $100.45   12.555%   $113.0615   $113.06   $113.05   $113.10  
  Purchase #2 $180.55   3.666%   $187.169   $187.17   $187.15   $187.20  
  Purchase #3 $244.59   10.510%   $270.2964   $270.30   $270.30   $270.30  
  Purchase #4 $105.31   13.218%   $119.2299   $119.23   $119.25   $119.20  
  Purchase #5 $111.72   9.194%   $121.9915   $121.99   $122.00   $122.00  
  Purchase #6 $13.31   5.813%   $14.0837   $14.08   $14.10   $14.10  
  Purchase #7 $198.63   5.555%   $209.6639   $209.66   $209.65   $209.70  
  7 purchase totals = $954.56       $1,035.4959   $1,035.49   $1,035.50   $1,035.60