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 $65.58   13.413%   $74.3762   $74.38   $74.40   $74.40  
  Purchase #2 $233.26   4.268%   $243.2155   $243.22   $243.20   $243.20  
  Purchase #3 $62.93   6.867%   $67.2514   $67.25   $67.25   $67.30  
  Purchase #4 $31.92   4.242%   $33.274   $33.27   $33.25   $33.30  
  Purchase #5 $58.79   12.318%   $66.0318   $66.03   $66.05   $66.00  
  Purchase #6 $142.64   8.111%   $154.2095   $154.21   $154.20   $154.20  
  Purchase #7 $145.98   7.777%   $157.3329   $157.33   $157.35   $157.30  
  7 purchase totals = $741.10       $795.6913   $795.69   $795.70   $795.70