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 $194.57   5.446%   $205.1663   $205.17   $205.15   $205.20  
  Purchase #2 $90.70   6.115%   $96.2463   $96.25   $96.25   $96.20  
  Purchase #3 $77.79   5.790%   $82.294   $82.29   $82.30   $82.30  
  Purchase #4 $13.43   9.262%   $14.6739   $14.67   $14.65   $14.70  
  Purchase #5 $79.47   6.105%   $84.3216   $84.32   $84.30   $84.30  
  Purchase #6 $56.52   7.872%   $60.9693   $60.97   $60.95   $61.00  
  Purchase #7 $53.72   9.667%   $58.9131   $58.91   $58.90   $58.90  
  7 purchase totals = $566.20       $602.5845   $602.58   $602.50   $602.60