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 $179.29   13.510%   $203.5121   $203.51   $203.50   $203.50  
  Purchase #2 $43.95   13.222%   $49.7611   $49.76   $49.75   $49.80  
  Purchase #3 $187.96   13.267%   $212.8967   $212.90   $212.90   $212.90  
  Purchase #4 $76.91   13.851%   $87.5628   $87.56   $87.55   $87.60  
  Purchase #5 $94.45   9.131%   $103.0742   $103.07   $103.05   $103.10  
  Purchase #6 $115.96   10.825%   $128.5127   $128.51   $128.50   $128.50  
  Purchase #7 $14.44   11.152%   $16.0503   $16.05   $16.05   $16.10  
  7 purchase totals = $712.96       $801.3699   $801.36   $801.30   $801.50