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 $115.59   5.751%   $122.2376   $122.24   $122.25   $122.20  
  Purchase #2 $246.88   12.747%   $278.3498   $278.35   $278.35   $278.30  
  Purchase #3 $146.25   7.485%   $157.1968   $157.20   $157.20   $157.20  
  Purchase #4 $217.83   7.467%   $234.0954   $234.10   $234.10   $234.10  
  Purchase #5 $183.27   12.108%   $205.4603   $205.46   $205.45   $205.50  
  Purchase #6 $22.76   13.794%   $25.8995   $25.90   $25.90   $25.90  
  Purchase #7 $63.52   13.477%   $72.0806   $72.08   $72.10   $72.10  
  7 purchase totals = $996.10       $1,095.3200   $1,095.33   $1,095.35   $1,095.30