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 $93.65   13.758%   $106.5344   $106.53   $106.55   $106.50  
  Purchase #2 $183.44   9.795%   $201.4079   $201.41   $201.40   $201.40  
  Purchase #3 $7.81   4.716%   $8.1783   $8.18   $8.20   $8.20  
  Purchase #4 $239.75   5.783%   $253.6147   $253.61   $253.60   $253.60  
  Purchase #5 $195.47   6.173%   $207.5364   $207.54   $207.55   $207.50  
  Purchase #6 $11.26   4.512%   $11.7681   $11.77   $11.75   $11.80  
  Purchase #7 $193.98   9.727%   $212.8484   $212.85   $212.85   $212.80  
  7 purchase totals = $925.36       $1,001.8882   $1,001.89   $1,001.90   $1,001.80