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 $241.80   9.572%   $264.9451   $264.95   $264.95   $264.90  
  Purchase #2 $105.39   6.803%   $112.5597   $112.56   $112.55   $112.60  
  Purchase #3 $97.75   9.757%   $107.2875   $107.29   $107.30   $107.30  
  Purchase #4 $201.78   5.368%   $212.6116   $212.61   $212.60   $212.60  
  Purchase #5 $10.65   3.523%   $11.0252   $11.03   $11.05   $11.00  
  Purchase #6 $73.93   5.654%   $78.11   $78.11   $78.10   $78.10  
  Purchase #7 $76.95   3.360%   $79.5355   $79.54   $79.55   $79.50  
  7 purchase totals = $808.25       $866.0746   $866.09   $866.10   $866.00