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 $86.70   13.424%   $98.3386   $98.34   $98.35   $98.30  
  Purchase #2 $245.38   11.222%   $272.9165   $272.92   $272.90   $272.90  
  Purchase #3 $31.43   10.248%   $34.6509   $34.65   $34.65   $34.70  
  Purchase #4 $135.40   3.162%   $139.6813   $139.68   $139.70   $139.70  
  Purchase #5 $106.77   11.789%   $119.3571   $119.36   $119.35   $119.40  
  Purchase #6 $205.31   10.370%   $226.6006   $226.60   $226.60   $226.60  
  Purchase #7 $155.93   4.246%   $162.5508   $162.55   $162.55   $162.60  
  7 purchase totals = $966.92       $1,054.0958   $1,054.10   $1,054.10   $1,054.20