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 $154.64   13.199%   $175.0509   $175.05   $175.05   $175.10  
  Purchase #2 $51.70   7.723%   $55.6928   $55.69   $55.70   $55.70  
  Purchase #3 $127.89   6.567%   $136.2885   $136.29   $136.30   $136.30  
  Purchase #4 $220.59   6.497%   $234.9217   $234.92   $234.90   $234.90  
  Purchase #5 $186.67   5.577%   $197.0806   $197.08   $197.10   $197.10  
  Purchase #6 $46.65   8.706%   $50.7113   $50.71   $50.70   $50.70  
  Purchase #7 $209.88   7.650%   $225.9358   $225.94   $225.95   $225.90  
  7 purchase totals = $998.02       $1,075.6816   $1,075.68   $1,075.70   $1,075.70