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 $227.55   10.527%   $251.5042   $251.50   $251.50   $251.50  
  Purchase #2 $117.93   13.695%   $134.0805   $134.08   $134.10   $134.10  
  Purchase #3 $58.36   4.720%   $61.1146   $61.11   $61.10   $61.10  
  Purchase #4 $171.85   5.735%   $181.7056   $181.71   $181.70   $181.70  
  Purchase #5 $103.54   11.695%   $115.649   $115.65   $115.65   $115.60  
  Purchase #6 $58.38   9.829%   $64.1182   $64.12   $64.10   $64.10  
  Purchase #7 $60.37   6.559%   $64.3297   $64.33   $64.35   $64.30  
  7 purchase totals = $797.98       $872.5018   $872.50   $872.50   $872.40