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 $46.80   11.368%   $52.1202   $52.12   $52.10   $52.10  
  Purchase #2 $151.81   9.120%   $165.6551   $165.66   $165.65   $165.70  
  Purchase #3 $133.68   5.490%   $141.019   $141.02   $141.00   $141.00  
  Purchase #4 $246.68   4.845%   $258.6316   $258.63   $258.65   $258.60  
  Purchase #5 $27.73   5.715%   $29.3148   $29.31   $29.30   $29.30  
  Purchase #6 $31.70   5.873%   $33.5617   $33.56   $33.55   $33.60  
  Purchase #7 $212.52   4.605%   $222.3065   $222.31   $222.30   $222.30  
  7 purchase totals = $850.92       $902.6089   $902.61   $902.55   $902.60