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 $192.26   8.292%   $208.2022   $208.20   $208.20   $208.20  
  Purchase #2 $60.79   5.815%   $64.3249   $64.32   $64.30   $64.30  
  Purchase #3 $15.55   11.183%   $17.289   $17.29   $17.30   $17.30  
  Purchase #4 $223.66   8.162%   $241.9151   $241.92   $241.90   $241.90  
  Purchase #5 $54.91   8.567%   $59.6141   $59.61   $59.60   $59.60  
  Purchase #6 $204.54   4.303%   $213.3414   $213.34   $213.35   $213.30  
  Purchase #7 $123.52   12.524%   $138.9896   $138.99   $139.00   $139.00  
  7 purchase totals = $875.23       $943.6763   $943.67   $943.65   $943.60