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 $156.29   7.676%   $168.2868   $168.29   $168.30   $168.30  
  Purchase #2 $34.56   13.590%   $39.2567   $39.26   $39.25   $39.30  
  Purchase #3 $25.49   7.798%   $27.4777   $27.48   $27.50   $27.50  
  Purchase #4 $61.52   7.510%   $66.1402   $66.14   $66.15   $66.10  
  Purchase #5 $214.94   4.634%   $224.9003   $224.90   $224.90   $224.90  
  Purchase #6 $92.82   8.582%   $100.7858   $100.79   $100.80   $100.80  
  Purchase #7 $65.77   5.279%   $69.242   $69.24   $69.25   $69.20  
  7 purchase totals = $651.39       $696.0895   $696.10   $696.15   $696.10