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 $156.76   5.603%   $165.5433   $165.54   $165.55   $165.50  
  Purchase #2 $158.53   9.284%   $173.2479   $173.25   $173.25   $173.20  
  Purchase #3 $236.31   8.751%   $256.9895   $256.99   $257.00   $257.00  
  Purchase #4 $79.57   6.846%   $85.0174   $85.02   $85.00   $85.00  
  Purchase #5 $42.42   6.501%   $45.1777   $45.18   $45.20   $45.20  
  Purchase #6 $186.69   8.544%   $202.6408   $202.64   $202.65   $202.60  
  Purchase #7 $104.79   4.650%   $109.6627   $109.66   $109.65   $109.70  
  7 purchase totals = $965.07       $1,038.2793   $1,038.28   $1,038.30   $1,038.20