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 $181.75   10.759%   $201.3045   $201.30   $201.30   $201.30  
  Purchase #2 $44.65   4.828%   $46.8057   $46.81   $46.80   $46.80  
  Purchase #3 $88.87   9.757%   $97.541   $97.54   $97.55   $97.50  
  Purchase #4 $152.33   5.475%   $160.6701   $160.67   $160.65   $160.70  
  Purchase #5 $236.91   4.654%   $247.9358   $247.94   $247.95   $247.90  
  Purchase #6 $109.57   13.455%   $124.3126   $124.31   $124.30   $124.30  
  Purchase #7 $40.95   6.403%   $43.572   $43.57   $43.55   $43.60  
  7 purchase totals = $855.03       $922.1417   $922.14   $922.10   $922.10