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 $111.83   6.433%   $119.024   $119.02   $119.00   $119.00  
  Purchase #2 $157.77   13.202%   $178.5988   $178.60   $178.60   $178.60  
  Purchase #3 $165.40   5.864%   $175.0991   $175.10   $175.10   $175.10  
  Purchase #4 $125.98   6.803%   $134.5504   $134.55   $134.55   $134.60  
  Purchase #5 $131.76   9.356%   $144.0875   $144.09   $144.10   $144.10  
  Purchase #6 $187.29   10.623%   $207.1858   $207.19   $207.20   $207.20  
  Purchase #7 $49.31   11.467%   $54.9644   $54.96   $54.95   $55.00  
  7 purchase totals = $929.34       $1,013.5100   $1,013.51   $1,013.50   $1,013.60