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 $157.59   11.526%   $175.7538   $175.75   $175.75   $175.80  
  Purchase #2 $197.74   10.522%   $218.5462   $218.55   $218.55   $218.50  
  Purchase #3 $71.80   12.257%   $80.6005   $80.60   $80.60   $80.60  
  Purchase #4 $51.37   6.425%   $54.6705   $54.67   $54.65   $54.70  
  Purchase #5 $104.94   4.421%   $109.5794   $109.58   $109.60   $109.60  
  Purchase #6 $178.31   3.723%   $184.9485   $184.95   $184.95   $184.90  
  Purchase #7 $91.70   4.232%   $95.5807   $95.58   $95.60   $95.60  
  7 purchase totals = $853.45       $919.6796   $919.68   $919.70   $919.70