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 $174.72   10.861%   $193.6963   $193.70   $193.70   $193.70  
  Purchase #2 $80.85   8.626%   $87.8241   $87.82   $87.80   $87.80  
  Purchase #3 $171.36   3.528%   $177.4056   $177.41   $177.40   $177.40  
  Purchase #4 $249.54   11.260%   $277.6382   $277.64   $277.65   $277.60  
  Purchase #5 $149.97   6.803%   $160.1725   $160.17   $160.15   $160.20  
  Purchase #6 $105.51   3.163%   $108.8473   $108.85   $108.85   $108.80  
  Purchase #7 $67.84   4.414%   $70.8345   $70.83   $70.85   $70.80  
  7 purchase totals = $999.79       $1,076.4185   $1,076.42   $1,076.40   $1,076.30