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 $51.48   11.831%   $57.5706   $57.57   $57.55   $57.60  
  Purchase #2 $77.43   13.274%   $87.7081   $87.71   $87.70   $87.70  
  Purchase #3 $124.61   5.869%   $131.9234   $131.92   $131.90   $131.90  
  Purchase #4 $88.91   5.437%   $93.744   $93.74   $93.75   $93.70  
  Purchase #5 $127.55   5.626%   $134.726   $134.73   $134.75   $134.70  
  Purchase #6 $174.85   13.350%   $198.1925   $198.19   $198.20   $198.20  
  Purchase #7 $117.45   3.873%   $121.9988   $122.00   $122.00   $122.00  
  7 purchase totals = $762.28       $825.8634   $825.86   $825.85   $825.80