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 $159.82   13.440%   $181.2998   $181.30   $181.30   $181.30  
  Purchase #2 $193.57   12.284%   $217.3481   $217.35   $217.35   $217.30  
  Purchase #3 $133.59   12.391%   $150.1431   $150.14   $150.15   $150.10  
  Purchase #4 $43.68   11.677%   $48.7805   $48.78   $48.80   $48.80  
  Purchase #5 $113.68   8.711%   $123.5827   $123.58   $123.60   $123.60  
  Purchase #6 $184.77   4.846%   $193.724   $193.72   $193.70   $193.70  
  Purchase #7 $28.48   9.329%   $31.1369   $31.14   $31.15   $31.10  
  7 purchase totals = $857.59       $946.0151   $946.01   $946.05   $945.90