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 $249.27   5.439%   $262.8278   $262.83   $262.85   $262.80  
  Purchase #2 $81.96   4.112%   $85.3302   $85.33   $85.35   $85.30  
  Purchase #3 $183.68   7.225%   $196.9509   $196.95   $196.95   $197.00  
  Purchase #4 $160.79   8.570%   $174.5697   $174.57   $174.55   $174.60  
  Purchase #5 $6.65   4.516%   $6.9503   $6.95   $6.95   $7.00  
  Purchase #6 $192.95   3.712%   $200.1123   $200.11   $200.10   $200.10  
  Purchase #7 $12.64   7.332%   $13.5668   $13.57   $13.55   $13.60  
  7 purchase totals = $887.94       $940.3080   $940.31   $940.30   $940.40