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 $56.68   11.605%   $63.2577   $63.26   $63.25   $63.30  
  Purchase #2 $102.26   7.708%   $110.1422   $110.14   $110.15   $110.10  
  Purchase #3 $168.53   7.378%   $180.9641   $180.96   $180.95   $181.00  
  Purchase #4 $233.76   11.136%   $259.7915   $259.79   $259.80   $259.80  
  Purchase #5 $154.28   4.723%   $161.5666   $161.57   $161.55   $161.60  
  Purchase #6 $10.75   9.373%   $11.7576   $11.76   $11.75   $11.80  
  Purchase #7 $157.79   10.298%   $174.0392   $174.04   $174.05   $174.00  
  7 purchase totals = $884.05       $961.5189   $961.52   $961.50   $961.60