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 $184.42   9.619%   $202.1594   $202.16   $202.15   $202.20  
  Purchase #2 $90.57   13.739%   $103.0134   $103.01   $103.00   $103.00  
  Purchase #3 $27.33   12.646%   $30.7862   $30.79   $30.80   $30.80  
  Purchase #4 $67.40   10.855%   $74.7163   $74.72   $74.70   $74.70  
  Purchase #5 $249.40   9.831%   $273.9185   $273.92   $273.90   $273.90  
  Purchase #6 $179.47   10.667%   $198.6141   $198.61   $198.60   $198.60  
  Purchase #7 $148.38   4.335%   $154.8123   $154.81   $154.80   $154.80  
  7 purchase totals = $946.97       $1,038.0202   $1,038.02   $1,037.95   $1,038.00