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 $136.99   11.392%   $152.5959   $152.60   $152.60   $152.60  
  Purchase #2 $15.80   9.316%   $17.2719   $17.27   $17.25   $17.30  
  Purchase #3 $240.26   5.724%   $254.0125   $254.01   $254.00   $254.00  
  Purchase #4 $137.69   13.740%   $156.6086   $156.61   $156.60   $156.60  
  Purchase #5 $180.40   12.581%   $203.0961   $203.10   $203.10   $203.10  
  Purchase #6 $22.49   5.563%   $23.7411   $23.74   $23.75   $23.70  
  Purchase #7 $233.86   5.274%   $246.1938   $246.19   $246.20   $246.20  
  7 purchase totals = $967.49       $1,053.5199   $1,053.52   $1,053.50   $1,053.50