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 $206.61   3.493%   $213.8269   $213.83   $213.85   $213.80  
  Purchase #2 $115.25   4.635%   $120.5918   $120.59   $120.60   $120.60  
  Purchase #3 $126.32   3.250%   $130.4254   $130.43   $130.45   $130.40  
  Purchase #4 $74.95   6.505%   $79.8255   $79.83   $79.85   $79.80  
  Purchase #5 $196.72   4.850%   $206.2609   $206.26   $206.25   $206.30  
  Purchase #6 $113.30   9.278%   $123.812   $123.81   $123.80   $123.80  
  Purchase #7 $65.52   4.160%   $68.2456   $68.25   $68.25   $68.20  
  7 purchase totals = $898.67       $942.9881   $943.00   $943.05   $942.90