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 $66.69   10.198%   $73.491   $73.49   $73.50   $73.50  
  Purchase #2 $52.98   6.770%   $56.5667   $56.57   $56.55   $56.60  
  Purchase #3 $87.65   7.233%   $93.9897   $93.99   $94.00   $94.00  
  Purchase #4 $202.70   3.326%   $209.4418   $209.44   $209.45   $209.40  
  Purchase #5 $123.27   13.780%   $140.2566   $140.26   $140.25   $140.30  
  Purchase #6 $71.52   8.678%   $77.7265   $77.73   $77.75   $77.70  
  Purchase #7 $184.61   8.654%   $200.5861   $200.59   $200.60   $200.60  
  7 purchase totals = $789.42       $852.0584   $852.07   $852.10   $852.10