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 $55.97   7.148%   $59.9707   $59.97   $59.95   $60.00  
  Purchase #2 $190.87   8.160%   $206.445   $206.45   $206.45   $206.40  
  Purchase #3 $240.56   10.587%   $266.0281   $266.03   $266.05   $266.00  
  Purchase #4 $199.85   9.209%   $218.2542   $218.25   $218.25   $218.30  
  Purchase #5 $31.35   8.402%   $33.984   $33.98   $34.00   $34.00  
  Purchase #6 $183.64   11.697%   $205.1204   $205.12   $205.10   $205.10  
  Purchase #7 $82.67   9.233%   $90.3029   $90.30   $90.30   $90.30  
  7 purchase totals = $984.91       $1,080.1053   $1,080.10   $1,080.10   $1,080.10