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 $86.34   6.470%   $91.9262   $91.93   $91.95   $91.90  
  Purchase #2 $186.42   9.239%   $203.6433   $203.64   $203.65   $203.60  
  Purchase #3 $97.67   11.287%   $108.694   $108.69   $108.70   $108.70  
  Purchase #4 $25.58   9.178%   $27.9277   $27.93   $27.95   $27.90  
  Purchase #5 $146.36   6.597%   $156.0154   $156.02   $156.00   $156.00  
  Purchase #6 $41.56   4.778%   $43.5457   $43.55   $43.55   $43.50  
  Purchase #7 $205.26   4.564%   $214.6281   $214.63   $214.65   $214.60  
  7 purchase totals = $789.19       $846.3804   $846.39   $846.45   $846.20