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 $168.43   7.462%   $180.9982   $181.00   $181.00   $181.00  
  Purchase #2 $149.90   11.153%   $166.6183   $166.62   $166.60   $166.60  
  Purchase #3 $222.96   5.824%   $235.9452   $235.95   $235.95   $235.90  
  Purchase #4 $220.36   11.331%   $245.329   $245.33   $245.35   $245.30  
  Purchase #5 $197.81   9.310%   $216.2261   $216.23   $216.25   $216.20  
  Purchase #6 $218.97   9.355%   $239.4546   $239.45   $239.45   $239.50  
  Purchase #7 $250.95   3.756%   $260.3757   $260.38   $260.40   $260.40  
  7 purchase totals = $1,429.38       $1,544.9471   $1,544.96   $1,545.00   $1,544.90