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 $63.86   10.677%   $70.6783   $70.68   $70.70   $70.70  
  Purchase #2 $124.35   9.551%   $136.2267   $136.23   $136.25   $136.20  
  Purchase #3 $131.51   10.643%   $145.5066   $145.51   $145.50   $145.50  
  Purchase #4 $216.27   4.545%   $226.0995   $226.10   $226.10   $226.10  
  Purchase #5 $118.26   12.845%   $133.4505   $133.45   $133.45   $133.50  
  Purchase #6 $150.83   6.237%   $160.2373   $160.24   $160.25   $160.20  
  Purchase #7 $219.54   9.123%   $239.5686   $239.57   $239.55   $239.60  
  7 purchase totals = $1,024.62       $1,111.7675   $1,111.78   $1,111.80   $1,111.80