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 $54.86   7.256%   $58.8406   $58.84   $58.85   $58.80  
  Purchase #2 $202.41   5.386%   $213.3118   $213.31   $213.30   $213.30  
  Purchase #3 $113.54   12.523%   $127.7586   $127.76   $127.75   $127.80  
  Purchase #4 $218.76   10.823%   $242.4364   $242.44   $242.45   $242.40  
  Purchase #5 $177.70   8.739%   $193.2292   $193.23   $193.25   $193.20  
  Purchase #6 $100.81   5.120%   $105.9715   $105.97   $105.95   $106.00  
  Purchase #7 $7.71   11.155%   $8.5701   $8.57   $8.55   $8.60  
  7 purchase totals = $875.79       $950.1182   $950.12   $950.10   $950.10