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 $156.79   13.313%   $177.6635   $177.66   $177.65   $177.70  
  Purchase #2 $15.79   12.397%   $17.7475   $17.75   $17.75   $17.70  
  Purchase #3 $210.54   12.515%   $236.8891   $236.89   $236.90   $236.90  
  Purchase #4 $59.50   3.178%   $61.3909   $61.39   $61.40   $61.40  
  Purchase #5 $70.49   12.591%   $79.3654   $79.37   $79.35   $79.40  
  Purchase #6 $232.29   5.273%   $244.5387   $244.54   $244.55   $244.50  
  Purchase #7 $232.67   3.708%   $241.2974   $241.30   $241.30   $241.30  
  7 purchase totals = $978.07       $1,058.8925   $1,058.90   $1,058.90   $1,058.90