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 $197.68   4.219%   $206.0201   $206.02   $206.00   $206.00  
  Purchase #2 $66.86   10.393%   $73.8088   $73.81   $73.80   $73.80  
  Purchase #3 $57.95   8.790%   $63.0438   $63.04   $63.05   $63.00  
  Purchase #4 $163.92   8.641%   $178.0843   $178.08   $178.10   $178.10  
  Purchase #5 $188.95   9.473%   $206.8492   $206.85   $206.85   $206.80  
  Purchase #6 $206.43   13.383%   $234.0565   $234.06   $234.05   $234.10  
  Purchase #7 $104.81   13.325%   $118.7759   $118.78   $118.80   $118.80  
  7 purchase totals = $986.60       $1,080.6386   $1,080.64   $1,080.65   $1,080.60