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 $146.26   12.832%   $165.0281   $165.03   $165.05   $165.00  
  Purchase #2 $167.91   4.434%   $175.3551   $175.36   $175.35   $175.40  
  Purchase #3 $89.88   13.712%   $102.2043   $102.20   $102.20   $102.20  
  Purchase #4 $119.35   5.602%   $126.036   $126.04   $126.05   $126.00  
  Purchase #5 $51.80   7.302%   $55.5824   $55.58   $55.60   $55.60  
  Purchase #6 $150.70   12.865%   $170.0876   $170.09   $170.10   $170.10  
  Purchase #7 $164.55   12.174%   $184.5823   $184.58   $184.60   $184.60  
  7 purchase totals = $890.45       $978.8758   $978.88   $978.95   $978.90