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 $161.73   13.853%   $184.1345   $184.13   $184.15   $184.10  
  Purchase #2 $114.56   7.361%   $122.9928   $122.99   $123.00   $123.00  
  Purchase #3 $54.36   5.546%   $57.3748   $57.37   $57.35   $57.40  
  Purchase #4 $61.88   8.495%   $67.1367   $67.14   $67.15   $67.10  
  Purchase #5 $147.71   8.679%   $160.5298   $160.53   $160.55   $160.50  
  Purchase #6 $138.82   10.558%   $153.4766   $153.48   $153.50   $153.50  
  Purchase #7 $238.45   9.401%   $260.8667   $260.87   $260.85   $260.90  
  7 purchase totals = $917.51       $1,006.5119   $1,006.51   $1,006.55   $1,006.50