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 $244.85   11.578%   $273.1987   $273.20   $273.20   $273.20  
  Purchase #2 $66.25   12.260%   $74.3723   $74.37   $74.35   $74.40  
  Purchase #3 $159.62   9.508%   $174.7967   $174.80   $174.80   $174.80  
  Purchase #4 $151.75   7.251%   $162.7534   $162.75   $162.75   $162.80  
  Purchase #5 $200.83   7.616%   $216.1252   $216.13   $216.15   $216.10  
  Purchase #6 $184.35   3.856%   $191.4585   $191.46   $191.45   $191.50  
  Purchase #7 $40.46   5.274%   $42.5939   $42.59   $42.60   $42.60  
  7 purchase totals = $1,048.11       $1,135.2987   $1,135.30   $1,135.30   $1,135.40