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 $216.72   13.653%   $246.3088   $246.31   $246.30   $246.30  
  Purchase #2 $222.45   8.718%   $241.8432   $241.84   $241.85   $241.80  
  Purchase #3 $218.94   7.467%   $235.2882   $235.29   $235.30   $235.30  
  Purchase #4 $21.98   9.429%   $24.0525   $24.05   $24.05   $24.10  
  Purchase #5 $115.26   6.295%   $122.5156   $122.52   $122.50   $122.50  
  Purchase #6 $103.62   4.737%   $108.5285   $108.53   $108.55   $108.50  
  Purchase #7 $206.66   3.347%   $213.5769   $213.58   $213.60   $213.60  
  7 purchase totals = $1,105.63       $1,192.1137   $1,192.12   $1,192.15   $1,192.10