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 $63.67   8.516%   $69.0921   $69.09   $69.10   $69.10  
  Purchase #2 $149.53   4.794%   $156.6985   $156.70   $156.70   $156.70  
  Purchase #3 $201.73   4.551%   $210.9107   $210.91   $210.90   $210.90  
  Purchase #4 $180.78   3.451%   $187.0187   $187.02   $187.00   $187.00  
  Purchase #5 $60.99   12.243%   $68.457   $68.46   $68.45   $68.50  
  Purchase #6 $126.97   12.394%   $142.7067   $142.71   $142.70   $142.70  
  Purchase #7 $238.32   8.147%   $257.7359   $257.74   $257.75   $257.70  
  7 purchase totals = $1,021.99       $1,092.6196   $1,092.63   $1,092.60   $1,092.60