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 $58.55   11.711%   $65.4068   $65.41   $65.40   $65.40  
  Purchase #2 $127.94   8.661%   $139.0209   $139.02   $139.00   $139.00  
  Purchase #3 $101.73   10.137%   $112.0424   $112.04   $112.05   $112.00  
  Purchase #4 $77.71   5.841%   $82.249   $82.25   $82.25   $82.20  
  Purchase #5 $202.91   13.581%   $230.4672   $230.47   $230.45   $230.50  
  Purchase #6 $197.67   8.187%   $213.8532   $213.85   $213.85   $213.90  
  Purchase #7 $175.64   3.327%   $181.4835   $181.48   $181.50   $181.50  
  7 purchase totals = $942.15       $1,024.5230   $1,024.52   $1,024.50   $1,024.50