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 $243.37   10.102%   $267.9552   $267.96   $267.95   $268.00  
  Purchase #2 $29.92   9.270%   $32.6936   $32.69   $32.70   $32.70  
  Purchase #3 $220.99   6.434%   $235.2085   $235.21   $235.20   $235.20  
  Purchase #4 $196.50   3.763%   $203.8943   $203.89   $203.90   $203.90  
  Purchase #5 $217.79   13.693%   $247.612   $247.61   $247.60   $247.60  
  Purchase #6 $59.52   4.436%   $62.1603   $62.16   $62.15   $62.20  
  Purchase #7 $231.43   5.462%   $244.0707   $244.07   $244.05   $244.10  
  7 purchase totals = $1,199.52       $1,293.5946   $1,293.59   $1,293.55   $1,293.70