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 $50.70   11.605%   $56.5837   $56.58   $56.60   $56.60  
  Purchase #2 $237.71   4.243%   $247.796   $247.80   $247.80   $247.80  
  Purchase #3 $79.46   10.771%   $88.0186   $88.02   $88.00   $88.00  
  Purchase #4 $150.65   13.582%   $171.1113   $171.11   $171.10   $171.10  
  Purchase #5 $98.97   10.340%   $109.2035   $109.20   $109.20   $109.20  
  Purchase #6 $164.96   12.650%   $185.8274   $185.83   $185.85   $185.80  
  Purchase #7 $147.63   7.338%   $158.4631   $158.46   $158.45   $158.50  
  7 purchase totals = $930.08       $1,017.0036   $1,017.00   $1,017.00   $1,017.00