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 $241.44   9.631%   $264.6931   $264.69   $264.70   $264.70  
  Purchase #2 $176.87   6.208%   $187.8501   $187.85   $187.85   $187.90  
  Purchase #3 $129.30   12.178%   $145.0462   $145.05   $145.05   $145.00  
  Purchase #4 $188.47   7.117%   $201.8834   $201.88   $201.90   $201.90  
  Purchase #5 $33.91   5.587%   $35.8046   $35.80   $35.80   $35.80  
  Purchase #6 $118.92   5.281%   $125.2002   $125.20   $125.20   $125.20  
  Purchase #7 $188.59   9.494%   $206.4947   $206.49   $206.50   $206.50  
  7 purchase totals = $1,077.50       $1,166.9723   $1,166.96   $1,167.00   $1,167.00