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 $86.61   9.774%   $95.0753   $95.08   $95.10   $95.10  
  Purchase #2 $193.35   4.660%   $202.3601   $202.36   $202.35   $202.40  
  Purchase #3 $188.30   11.535%   $210.0204   $210.02   $210.00   $210.00  
  Purchase #4 $74.62   4.512%   $77.9869   $77.99   $78.00   $78.00  
  Purchase #5 $15.28   8.466%   $16.5736   $16.57   $16.55   $16.60  
  Purchase #6 $171.26   13.281%   $194.005   $194.01   $194.00   $194.00  
  Purchase #7 $136.32   5.581%   $143.928   $143.93   $143.95   $143.90  
  7 purchase totals = $865.74       $939.9493   $939.96   $939.95   $940.00