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 $226.41   6.787%   $241.7764   $241.78   $241.80   $241.80  
  Purchase #2 $161.58   11.743%   $180.5543   $180.55   $180.55   $180.60  
  Purchase #3 $30.49   11.703%   $34.0582   $34.06   $34.05   $34.10  
  Purchase #4 $214.66   13.721%   $244.1135   $244.11   $244.10   $244.10  
  Purchase #5 $221.31   3.570%   $229.2108   $229.21   $229.20   $229.20  
  Purchase #6 $61.29   11.741%   $68.4861   $68.49   $68.50   $68.50  
  Purchase #7 $247.75   7.343%   $265.9423   $265.94   $265.95   $265.90  
  7 purchase totals = $1,163.49       $1,264.1416   $1,264.14   $1,264.15   $1,264.20