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 $60.81   4.693%   $63.6638   $63.66   $63.65   $63.70  
  Purchase #2 $191.50   5.465%   $201.9655   $201.97   $201.95   $202.00  
  Purchase #3 $203.35   5.182%   $213.8876   $213.89   $213.90   $213.90  
  Purchase #4 $217.40   13.850%   $247.5099   $247.51   $247.50   $247.50  
  Purchase #5 $242.48   8.367%   $262.7683   $262.77   $262.75   $262.80  
  Purchase #6 $202.64   8.144%   $219.143   $219.14   $219.15   $219.10  
  Purchase #7 $199.41   3.310%   $206.0105   $206.01   $206.00   $206.00  
  7 purchase totals = $1,317.59       $1,414.9486   $1,414.95   $1,414.90   $1,415.00