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 $118.65   5.626%   $125.3252   $125.33   $125.35   $125.30  
  Purchase #2 $45.89   6.574%   $48.9068   $48.91   $48.90   $48.90  
  Purchase #3 $169.68   4.734%   $177.7127   $177.71   $177.70   $177.70  
  Purchase #4 $52.54   13.835%   $59.8089   $59.81   $59.80   $59.80  
  Purchase #5 $199.91   4.668%   $209.2418   $209.24   $209.25   $209.20  
  Purchase #6 $29.79   12.767%   $33.5933   $33.59   $33.60   $33.60  
  Purchase #7 $223.64   12.551%   $251.7091   $251.71   $251.70   $251.70  
  7 purchase totals = $840.10       $906.2978   $906.30   $906.30   $906.20