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 $103.89   11.636%   $115.9786   $115.98   $116.00   $116.00  
  Purchase #2 $247.89   7.849%   $267.3469   $267.35   $267.35   $267.30  
  Purchase #3 $225.48   5.202%   $237.2095   $237.21   $237.20   $237.20  
  Purchase #4 $36.34   7.184%   $38.9507   $38.95   $38.95   $39.00  
  Purchase #5 $171.26   12.309%   $192.3404   $192.34   $192.35   $192.30  
  Purchase #6 $53.32   4.380%   $55.6554   $55.66   $55.65   $55.70  
  Purchase #7 $6.83   7.701%   $7.356   $7.36   $7.35   $7.40  
  7 purchase totals = $845.01       $914.8375   $914.85   $914.85   $914.90