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 $193.47   6.372%   $205.7979   $205.80   $205.80   $205.80  
  Purchase #2 $64.96   7.189%   $69.63   $69.63   $69.65   $69.60  
  Purchase #3 $16.31   5.657%   $17.2327   $17.23   $17.25   $17.20  
  Purchase #4 $158.68   13.487%   $180.0812   $180.08   $180.10   $180.10  
  Purchase #5 $187.68   12.569%   $211.2695   $211.27   $211.25   $211.30  
  Purchase #6 $195.69   13.341%   $221.797   $221.80   $221.80   $221.80  
  Purchase #7 $133.36   12.199%   $149.6286   $149.63   $149.65   $149.60  
  7 purchase totals = $950.15       $1,055.4369   $1,055.44   $1,055.50   $1,055.40