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 $183.94   11.777%   $205.6026   $205.60   $205.60   $205.60  
  Purchase #2 $170.69   8.303%   $184.8624   $184.86   $184.85   $184.90  
  Purchase #3 $158.68   6.504%   $169.0005   $169.00   $169.00   $169.00  
  Purchase #4 $30.97   9.390%   $33.8781   $33.88   $33.90   $33.90  
  Purchase #5 $79.96   3.874%   $83.0577   $83.06   $83.05   $83.10  
  Purchase #6 $207.76   3.466%   $214.961   $214.96   $214.95   $215.00  
  Purchase #7 $110.74   8.378%   $120.0178   $120.02   $120.00   $120.00  
  7 purchase totals = $942.74       $1,011.3801   $1,011.38   $1,011.35   $1,011.50