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 $51.83   12.492%   $58.3046   $58.30   $58.30   $58.30  
  Purchase #2 $183.29   6.538%   $195.2735   $195.27   $195.25   $195.30  
  Purchase #3 $225.94   5.386%   $238.1091   $238.11   $238.10   $238.10  
  Purchase #4 $195.34   11.862%   $218.5112   $218.51   $218.50   $218.50  
  Purchase #5 $5.63   7.188%   $6.0347   $6.03   $6.05   $6.00  
  Purchase #6 $173.87   11.395%   $193.6825   $193.68   $193.70   $193.70  
  Purchase #7 $50.67   11.805%   $56.6516   $56.65   $56.65   $56.70  
  7 purchase totals = $886.57       $966.5672   $966.55   $966.55   $966.60