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 $233.67   6.378%   $248.5735   $248.57   $248.55   $248.60  
  Purchase #2 $26.32   3.435%   $27.2241   $27.22   $27.20   $27.20  
  Purchase #3 $196.71   6.635%   $209.7617   $209.76   $209.75   $209.80  
  Purchase #4 $97.29   13.126%   $110.0603   $110.06   $110.05   $110.10  
  Purchase #5 $67.93   9.330%   $74.2679   $74.27   $74.25   $74.30  
  Purchase #6 $86.74   5.506%   $91.5159   $91.52   $91.50   $91.50  
  Purchase #7 $160.59   5.751%   $169.8255   $169.83   $169.85   $169.80  
  7 purchase totals = $869.25       $931.2289   $931.23   $931.15   $931.30