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 $46.48   13.121%   $52.5786   $52.58   $52.60   $52.60  
  Purchase #2 $95.44   12.736%   $107.5952   $107.60   $107.60   $107.60  
  Purchase #3 $35.72   5.649%   $37.7378   $37.74   $37.75   $37.70  
  Purchase #4 $234.56   6.429%   $249.6399   $249.64   $249.65   $249.60  
  Purchase #5 $32.92   6.289%   $34.9903   $34.99   $35.00   $35.00  
  Purchase #6 $210.84   10.214%   $232.3752   $232.38   $232.40   $232.40  
  Purchase #7 $7.52   13.477%   $8.5335   $8.53   $8.55   $8.50  
  7 purchase totals = $663.48       $723.4505   $723.46   $723.55   $723.40