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 $65.56   5.606%   $69.2353   $69.24   $69.25   $69.20  
  Purchase #2 $23.42   10.754%   $25.9386   $25.94   $25.95   $25.90  
  Purchase #3 $199.62   12.367%   $224.307   $224.31   $224.30   $224.30  
  Purchase #4 $129.81   7.509%   $139.5574   $139.56   $139.55   $139.60  
  Purchase #5 $206.51   11.721%   $230.715   $230.72   $230.70   $230.70  
  Purchase #6 $49.91   7.403%   $53.6048   $53.60   $53.60   $53.60  
  Purchase #7 $177.52   8.686%   $192.9394   $192.94   $192.95   $192.90  
  7 purchase totals = $852.35       $936.2975   $936.31   $936.30   $936.20