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 $119.91   6.155%   $127.2905   $127.29   $127.30   $127.30  
  Purchase #2 $87.68   4.189%   $91.3529   $91.35   $91.35   $91.40  
  Purchase #3 $199.80   13.518%   $226.809   $226.81   $226.80   $226.80  
  Purchase #4 $246.57   11.302%   $274.4373   $274.44   $274.45   $274.40  
  Purchase #5 $87.83   6.792%   $93.7954   $93.80   $93.80   $93.80  
  Purchase #6 $157.32   6.269%   $167.1824   $167.18   $167.20   $167.20  
  Purchase #7 $70.84   7.802%   $76.3669   $76.37   $76.35   $76.40  
  7 purchase totals = $969.95       $1,057.2344   $1,057.24   $1,057.25   $1,057.30