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 $159.53   10.672%   $176.555   $176.56   $176.55   $176.60  
  Purchase #2 $16.78   5.356%   $17.6787   $17.68   $17.70   $17.70  
  Purchase #3 $204.84   5.452%   $216.0079   $216.01   $216.00   $216.00  
  Purchase #4 $176.66   13.820%   $201.0744   $201.07   $201.05   $201.10  
  Purchase #5 $187.90   5.657%   $198.5295   $198.53   $198.55   $198.50  
  Purchase #6 $119.97   5.614%   $126.7051   $126.71   $126.70   $126.70  
  Purchase #7 $48.49   3.359%   $50.1188   $50.12   $50.10   $50.10  
  7 purchase totals = $914.17       $986.6694   $986.68   $986.65   $986.70