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 $138.68   10.424%   $153.136   $153.14   $153.15   $153.10  
  Purchase #2 $51.27   8.818%   $55.791   $55.79   $55.80   $55.80  
  Purchase #3 $77.71   6.353%   $82.6469   $82.65   $82.65   $82.60  
  Purchase #4 $101.56   12.383%   $114.1362   $114.14   $114.15   $114.10  
  Purchase #5 $128.94   13.582%   $146.4526   $146.45   $146.45   $146.50  
  Purchase #6 $238.83   4.729%   $250.1243   $250.12   $250.10   $250.10  
  Purchase #7 $170.35   9.345%   $186.2692   $186.27   $186.25   $186.30  
  7 purchase totals = $907.34       $988.5562   $988.56   $988.55   $988.50