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 $53.25   9.548%   $58.3343   $58.33   $58.35   $58.30  
  Purchase #2 $222.87   10.312%   $245.8524   $245.85   $245.85   $245.90  
  Purchase #3 $86.74   9.813%   $95.2518   $95.25   $95.25   $95.30  
  Purchase #4 $67.47   9.231%   $73.6982   $73.70   $73.70   $73.70  
  Purchase #5 $239.81   8.441%   $260.0524   $260.05   $260.05   $260.10  
  Purchase #6 $147.53   3.130%   $152.1477   $152.15   $152.15   $152.10  
  Purchase #7 $5.52   6.329%   $5.8694   $5.87   $5.85   $5.90  
  7 purchase totals = $823.19       $891.2062   $891.20   $891.20   $891.30