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 $61.74   6.861%   $65.976   $65.98   $66.00   $66.00  
  Purchase #2 $70.95   5.560%   $74.8948   $74.89   $74.90   $74.90  
  Purchase #3 $96.69   9.237%   $105.6213   $105.62   $105.60   $105.60  
  Purchase #4 $5.61   7.348%   $6.0222   $6.02   $6.00   $6.00  
  Purchase #5 $26.82   4.233%   $27.9553   $27.96   $27.95   $28.00  
  Purchase #6 $216.65   3.241%   $223.6716   $223.67   $223.65   $223.70  
  Purchase #7 $226.72   11.429%   $252.6318   $252.63   $252.65   $252.60  
  7 purchase totals = $705.18       $756.7730   $756.77   $756.75   $756.80