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 $197.63   4.717%   $206.9522   $206.95   $206.95   $207.00  
  Purchase #2 $178.68   6.297%   $189.9315   $189.93   $189.95   $189.90  
  Purchase #3 $35.84   7.742%   $38.6147   $38.61   $38.60   $38.60  
  Purchase #4 $94.57   3.751%   $98.1173   $98.12   $98.10   $98.10  
  Purchase #5 $164.53   4.869%   $172.541   $172.54   $172.55   $172.50  
  Purchase #6 $53.37   11.384%   $59.4456   $59.45   $59.45   $59.40  
  Purchase #7 $52.29   3.630%   $54.1881   $54.19   $54.20   $54.20  
  7 purchase totals = $776.91       $819.7904   $819.79   $819.80   $819.70