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 $60.48   10.553%   $66.8625   $66.86   $66.85   $66.90  
  Purchase #2 $186.91   12.731%   $210.7055   $210.71   $210.70   $210.70  
  Purchase #3 $49.55   5.481%   $52.2658   $52.27   $52.25   $52.30  
  Purchase #4 $21.94   6.139%   $23.2869   $23.29   $23.30   $23.30  
  Purchase #5 $174.90   9.811%   $192.0594   $192.06   $192.05   $192.10  
  Purchase #6 $74.56   9.331%   $81.5172   $81.52   $81.50   $81.50  
  Purchase #7 $238.43   13.206%   $269.9171   $269.92   $269.90   $269.90  
  7 purchase totals = $806.77       $896.6144   $896.63   $896.55   $896.70