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 $48.34   13.830%   $55.0254   $55.03   $55.05   $55.00  
  Purchase #2 $96.51   11.445%   $107.5556   $107.56   $107.55   $107.60  
  Purchase #3 $95.81   12.720%   $107.997   $108.00   $108.00   $108.00  
  Purchase #4 $232.45   5.262%   $244.6815   $244.68   $244.70   $244.70  
  Purchase #5 $25.88   12.127%   $29.0185   $29.02   $29.00   $29.00  
  Purchase #6 $242.80   9.654%   $266.2399   $266.24   $266.25   $266.20  
  Purchase #7 $48.62   4.529%   $50.822   $50.82   $50.80   $50.80  
  7 purchase totals = $790.41       $861.3399   $861.35   $861.35   $861.30