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 $209.55   8.575%   $227.5189   $227.52   $227.50   $227.50  
  Purchase #2 $56.57   10.813%   $62.6869   $62.69   $62.70   $62.70  
  Purchase #3 $49.79   4.854%   $52.2068   $52.21   $52.20   $52.20  
  Purchase #4 $140.46   5.557%   $148.2654   $148.27   $148.25   $148.30  
  Purchase #5 $11.35   13.473%   $12.8792   $12.88   $12.90   $12.90  
  Purchase #6 $205.65   8.747%   $223.6382   $223.64   $223.65   $223.60  
  Purchase #7 $192.51   7.392%   $206.7403   $206.74   $206.75   $206.70  
  7 purchase totals = $865.88       $933.9357   $933.95   $933.95   $933.90