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 $46.86   12.546%   $52.7391   $52.74   $52.75   $52.70  
  Purchase #2 $227.25   10.873%   $251.9589   $251.96   $251.95   $252.00  
  Purchase #3 $116.48   9.498%   $127.5433   $127.54   $127.55   $127.50  
  Purchase #4 $212.95   5.360%   $224.3641   $224.36   $224.35   $224.40  
  Purchase #5 $133.66   6.311%   $142.0953   $142.10   $142.10   $142.10  
  Purchase #6 $133.45   8.618%   $144.9507   $144.95   $144.95   $145.00  
  Purchase #7 $172.88   3.451%   $178.8461   $178.85   $178.85   $178.80  
  7 purchase totals = $1,043.53       $1,122.4975   $1,122.50   $1,122.50   $1,122.50