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 $111.86   10.214%   $123.2854   $123.29   $123.30   $123.30  
  Purchase #2 $65.96   12.117%   $73.9524   $73.95   $73.95   $74.00  
  Purchase #3 $174.37   11.236%   $193.9622   $193.96   $193.95   $194.00  
  Purchase #4 $57.75   8.667%   $62.7552   $62.76   $62.75   $62.80  
  Purchase #5 $228.59   7.846%   $246.5252   $246.53   $246.55   $246.50  
  Purchase #6 $249.52   3.141%   $257.3574   $257.36   $257.35   $257.40  
  Purchase #7 $99.85   5.864%   $105.7052   $105.71   $105.70   $105.70  
  7 purchase totals = $987.90       $1,063.5430   $1,063.56   $1,063.55   $1,063.70