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 $202.79   6.825%   $216.6304   $216.63   $216.65   $216.60  
  Purchase #2 $47.26   10.144%   $52.0541   $52.05   $52.05   $52.10  
  Purchase #3 $20.86   13.570%   $23.6907   $23.69   $23.70   $23.70  
  Purchase #4 $66.58   5.815%   $70.4516   $70.45   $70.45   $70.50  
  Purchase #5 $247.32   7.261%   $265.2779   $265.28   $265.30   $265.30  
  Purchase #6 $216.50   11.300%   $240.9645   $240.96   $240.95   $241.00  
  Purchase #7 $150.27   4.821%   $157.5145   $157.51   $157.50   $157.50  
  7 purchase totals = $951.58       $1,026.5837   $1,026.57   $1,026.60   $1,026.70