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 $61.25   9.687%   $67.1833   $67.18   $67.20   $67.20  
  Purchase #2 $47.64   13.186%   $53.9218   $53.92   $53.90   $53.90  
  Purchase #3 $145.42   11.158%   $161.646   $161.65   $161.65   $161.60  
  Purchase #4 $139.49   11.397%   $155.3877   $155.39   $155.40   $155.40  
  Purchase #5 $210.25   5.873%   $222.598   $222.60   $222.60   $222.60  
  Purchase #6 $201.96   4.473%   $210.9937   $210.99   $211.00   $211.00  
  Purchase #7 $128.31   12.386%   $144.2025   $144.20   $144.20   $144.20  
  7 purchase totals = $934.32       $1,015.9330   $1,015.93   $1,015.95   $1,015.90