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 $55.44   6.133%   $58.8401   $58.84   $58.85   $58.80  
  Purchase #2 $217.37   8.547%   $235.9486   $235.95   $235.95   $235.90  
  Purchase #3 $96.32   10.841%   $106.7621   $106.76   $106.75   $106.80  
  Purchase #4 $197.54   9.550%   $216.4051   $216.41   $216.40   $216.40  
  Purchase #5 $120.60   13.683%   $137.1017   $137.10   $137.10   $137.10  
  Purchase #6 $212.26   4.315%   $221.419   $221.42   $221.40   $221.40  
  Purchase #7 $40.71   5.596%   $42.9881   $42.99   $43.00   $43.00  
  7 purchase totals = $940.24       $1,019.4647   $1,019.47   $1,019.45   $1,019.40