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 $57.68   10.398%   $63.6776   $63.68   $63.70   $63.70  
  Purchase #2 $215.66   4.371%   $225.0865   $225.09   $225.10   $225.10  
  Purchase #3 $179.31   10.323%   $197.8202   $197.82   $197.80   $197.80  
  Purchase #4 $121.78   4.352%   $127.0799   $127.08   $127.10   $127.10  
  Purchase #5 $77.25   10.672%   $85.4941   $85.49   $85.50   $85.50  
  Purchase #6 $188.45   3.139%   $194.3654   $194.37   $194.35   $194.40  
  Purchase #7 $122.69   9.236%   $134.0216   $134.02   $134.00   $134.00  
  7 purchase totals = $962.82       $1,027.5453   $1,027.55   $1,027.55   $1,027.60