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 $242.61   13.681%   $275.8015   $275.80   $275.80   $275.80  
  Purchase #2 $71.58   12.223%   $80.3292   $80.33   $80.35   $80.30  
  Purchase #3 $172.76   5.411%   $182.108   $182.11   $182.10   $182.10  
  Purchase #4 $234.87   8.292%   $254.3454   $254.35   $254.35   $254.30  
  Purchase #5 $131.67   12.325%   $147.8983   $147.90   $147.90   $147.90  
  Purchase #6 $249.77   6.758%   $266.6495   $266.65   $266.65   $266.60  
  Purchase #7 $229.50   11.196%   $255.1948   $255.19   $255.20   $255.20  
  7 purchase totals = $1,332.76       $1,462.3267   $1,462.33   $1,462.35   $1,462.20