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 $192.35   7.198%   $206.1954   $206.20   $206.20   $206.20  
  Purchase #2 $244.28   10.714%   $270.4522   $270.45   $270.45   $270.50  
  Purchase #3 $210.40   9.114%   $229.5759   $229.58   $229.60   $229.60  
  Purchase #4 $32.29   11.736%   $36.0796   $36.08   $36.10   $36.10  
  Purchase #5 $218.46   9.468%   $239.1438   $239.14   $239.15   $239.10  
  Purchase #6 $77.81   10.259%   $85.7925   $85.79   $85.80   $85.80  
  Purchase #7 $157.45   10.549%   $174.0594   $174.06   $174.05   $174.10  
  7 purchase totals = $1,133.04       $1,241.2988   $1,241.30   $1,241.35   $1,241.40