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 $232.99   12.853%   $262.9362   $262.94   $262.95   $262.90  
  Purchase #2 $195.39   13.459%   $221.6875   $221.69   $221.70   $221.70  
  Purchase #3 $111.75   5.370%   $117.751   $117.75   $117.75   $117.80  
  Purchase #4 $67.52   6.844%   $72.1411   $72.14   $72.15   $72.10  
  Purchase #5 $91.71   11.662%   $102.4052   $102.41   $102.40   $102.40  
  Purchase #6 $215.61   7.635%   $232.0718   $232.07   $232.05   $232.10  
  Purchase #7 $82.67   5.329%   $87.0755   $87.08   $87.10   $87.10  
  7 purchase totals = $997.64       $1,096.0683   $1,096.08   $1,096.10   $1,096.10