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 $243.92   11.776%   $272.644   $272.64   $272.65   $272.60  
  Purchase #2 $58.25   5.197%   $61.2773   $61.28   $61.30   $61.30  
  Purchase #3 $200.30   13.225%   $226.7897   $226.79   $226.80   $226.80  
  Purchase #4 $115.84   11.616%   $129.296   $129.30   $129.30   $129.30  
  Purchase #5 $7.31   10.199%   $8.0555   $8.06   $8.05   $8.10  
  Purchase #6 $207.95   13.338%   $235.6864   $235.69   $235.70   $235.70  
  Purchase #7 $249.82   7.346%   $268.1718   $268.17   $268.15   $268.20  
  7 purchase totals = $1,083.39       $1,201.9207   $1,201.93   $1,201.95   $1,202.00