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 $132.43   9.253%   $144.6837   $144.68   $144.70   $144.70  
  Purchase #2 $175.39   9.399%   $191.8749   $191.87   $191.85   $191.90  
  Purchase #3 $85.37   12.522%   $96.06   $96.06   $96.05   $96.10  
  Purchase #4 $71.92   4.116%   $74.8802   $74.88   $74.90   $74.90  
  Purchase #5 $123.39   10.251%   $136.0387   $136.04   $136.05   $136.00  
  Purchase #6 $249.82   3.435%   $258.4013   $258.40   $258.40   $258.40  
  Purchase #7 $174.51   10.159%   $192.2385   $192.24   $192.25   $192.20  
  7 purchase totals = $1,012.83       $1,094.1773   $1,094.17   $1,094.20   $1,094.20