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 $93.86   6.153%   $99.6352   $99.64   $99.65   $99.60  
  Purchase #2 $224.45   4.265%   $234.0228   $234.02   $234.00   $234.00  
  Purchase #3 $39.55   4.291%   $41.2471   $41.25   $41.25   $41.20  
  Purchase #4 $69.67   11.359%   $77.5838   $77.58   $77.60   $77.60  
  Purchase #5 $216.91   5.292%   $228.3889   $228.39   $228.40   $228.40  
  Purchase #6 $108.64   8.597%   $117.9798   $117.98   $118.00   $118.00  
  Purchase #7 $148.35   4.648%   $155.2453   $155.25   $155.25   $155.20  
  7 purchase totals = $901.43       $954.1029   $954.11   $954.15   $954.00