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 $56.35   6.440%   $59.9789   $59.98   $60.00   $60.00  
  Purchase #2 $196.25   7.721%   $211.4025   $211.40   $211.40   $211.40  
  Purchase #3 $86.93   5.858%   $92.0224   $92.02   $92.00   $92.00  
  Purchase #4 $84.61   4.802%   $88.673   $88.67   $88.65   $88.70  
  Purchase #5 $101.81   13.284%   $115.3344   $115.33   $115.35   $115.30  
  Purchase #6 $206.62   11.159%   $229.6767   $229.68   $229.70   $229.70  
  Purchase #7 $110.80   6.137%   $117.5998   $117.60   $117.60   $117.60  
  7 purchase totals = $843.37       $914.6877   $914.68   $914.70   $914.70