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 $130.56   11.462%   $145.5248   $145.52   $145.50   $145.50  
  Purchase #2 $187.25   4.845%   $196.3223   $196.32   $196.30   $196.30  
  Purchase #3 $55.40   8.300%   $59.9982   $60.00   $60.00   $60.00  
  Purchase #4 $212.67   11.461%   $237.0441   $237.04   $237.05   $237.00  
  Purchase #5 $48.50   12.701%   $54.66   $54.66   $54.65   $54.70  
  Purchase #6 $28.64   12.412%   $32.1948   $32.19   $32.20   $32.20  
  Purchase #7 $175.33   13.351%   $198.7383   $198.74   $198.75   $198.70  
  7 purchase totals = $838.35       $924.4825   $924.47   $924.45   $924.40