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 $49.65   8.451%   $53.8459   $53.85   $53.85   $53.80  
  Purchase #2 $228.63   11.398%   $254.6892   $254.69   $254.70   $254.70  
  Purchase #3 $235.77   4.246%   $245.7808   $245.78   $245.80   $245.80  
  Purchase #4 $106.30   3.665%   $110.1959   $110.20   $110.20   $110.20  
  Purchase #5 $107.96   11.157%   $120.0051   $120.01   $120.00   $120.00  
  Purchase #6 $176.72   7.102%   $189.2707   $189.27   $189.25   $189.30  
  Purchase #7 $127.74   11.112%   $141.9345   $141.93   $141.95   $141.90  
  7 purchase totals = $1,032.77       $1,115.7221   $1,115.73   $1,115.75   $1,115.70