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 $246.54   8.708%   $268.0087   $268.01   $268.00   $268.00  
  Purchase #2 $62.90   9.225%   $68.7025   $68.70   $68.70   $68.70  
  Purchase #3 $149.73   12.333%   $168.1962   $168.20   $168.20   $168.20  
  Purchase #4 $236.33   9.202%   $258.0771   $258.08   $258.10   $258.10  
  Purchase #5 $16.88   8.860%   $18.3756   $18.38   $18.40   $18.40  
  Purchase #6 $31.45   6.484%   $33.4892   $33.49   $33.50   $33.50  
  Purchase #7 $221.35   4.860%   $232.1076   $232.11   $232.10   $232.10  
  7 purchase totals = $965.18       $1,046.9569   $1,046.97   $1,047.00   $1,047.00