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 $244.93   12.676%   $275.9773   $275.98   $276.00   $276.00  
  Purchase #2 $84.82   13.159%   $95.9815   $95.98   $96.00   $96.00  
  Purchase #3 $143.39   3.851%   $148.9119   $148.91   $148.90   $148.90  
  Purchase #4 $114.92   7.374%   $123.3942   $123.39   $123.40   $123.40  
  Purchase #5 $64.44   10.753%   $71.3692   $71.37   $71.35   $71.40  
  Purchase #6 $198.77   11.790%   $222.205   $222.21   $222.20   $222.20  
  Purchase #7 $178.69   7.470%   $192.0381   $192.04   $192.05   $192.00  
  7 purchase totals = $1,029.96       $1,129.8772   $1,129.88   $1,129.90   $1,129.90