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 $222.65   6.744%   $237.6655   $237.67   $237.65   $237.70  
  Purchase #2 $75.85   12.758%   $85.5269   $85.53   $85.55   $85.50  
  Purchase #3 $124.39   8.377%   $134.8102   $134.81   $134.80   $134.80  
  Purchase #4 $79.67   10.813%   $88.2847   $88.28   $88.30   $88.30  
  Purchase #5 $201.87   5.606%   $213.1868   $213.19   $213.20   $213.20  
  Purchase #6 $200.44   4.840%   $210.1413   $210.14   $210.15   $210.10  
  Purchase #7 $42.94   7.549%   $46.1815   $46.18   $46.20   $46.20  
  7 purchase totals = $947.81       $1,015.7969   $1,015.80   $1,015.85   $1,015.80