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 $59.42   9.237%   $64.9086   $64.91   $64.90   $64.90  
  Purchase #2 $239.34   7.334%   $256.8932   $256.89   $256.90   $256.90  
  Purchase #3 $66.39   4.771%   $69.5575   $69.56   $69.55   $69.60  
  Purchase #4 $250.33   5.207%   $263.3647   $263.36   $263.35   $263.40  
  Purchase #5 $250.55   12.544%   $281.979   $281.98   $282.00   $282.00  
  Purchase #6 $238.50   10.213%   $262.858   $262.86   $262.85   $262.90  
  Purchase #7 $208.52   11.752%   $233.0253   $233.03   $233.05   $233.00  
  7 purchase totals = $1,313.05       $1,432.5863   $1,432.59   $1,432.60   $1,432.70