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 $61.77   11.691%   $68.9915   $68.99   $69.00   $69.00  
  Purchase #2 $51.51   4.281%   $53.7151   $53.72   $53.70   $53.70  
  Purchase #3 $146.44   11.179%   $162.8105   $162.81   $162.80   $162.80  
  Purchase #4 $51.59   5.451%   $54.4022   $54.40   $54.40   $54.40  
  Purchase #5 $129.74   9.137%   $141.5943   $141.59   $141.60   $141.60  
  Purchase #6 $209.43   6.480%   $223.0011   $223.00   $223.00   $223.00  
  Purchase #7 $181.53   10.770%   $201.0808   $201.08   $201.10   $201.10  
  7 purchase totals = $832.01       $905.5955   $905.59   $905.60   $905.60