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 $110.95   10.757%   $122.8849   $122.88   $122.90   $122.90  
  Purchase #2 $55.62   12.194%   $62.4023   $62.40   $62.40   $62.40  
  Purchase #3 $124.86   6.209%   $132.6126   $132.61   $132.60   $132.60  
  Purchase #4 $240.89   4.835%   $252.537   $252.54   $252.55   $252.50  
  Purchase #5 $246.52   9.783%   $270.6371   $270.64   $270.65   $270.60  
  Purchase #6 $127.68   4.569%   $133.5137   $133.51   $133.50   $133.50  
  Purchase #7 $130.94   13.614%   $148.7662   $148.77   $148.75   $148.80  
  7 purchase totals = $1,037.46       $1,123.3538   $1,123.35   $1,123.35   $1,123.30