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 $53.74   5.368%   $56.6248   $56.62   $56.60   $56.60  
  Purchase #2 $206.84   6.326%   $219.9247   $219.92   $219.90   $219.90  
  Purchase #3 $218.48   7.869%   $235.6722   $235.67   $235.65   $235.70  
  Purchase #4 $177.95   11.641%   $198.6652   $198.67   $198.65   $198.70  
  Purchase #5 $53.97   4.302%   $56.2918   $56.29   $56.30   $56.30  
  Purchase #6 $182.42   7.730%   $196.5211   $196.52   $196.50   $196.50  
  Purchase #7 $232.44   7.727%   $250.4006   $250.40   $250.40   $250.40  
  7 purchase totals = $1,125.84       $1,214.1004   $1,214.09   $1,214.00   $1,214.10