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 $61.40   7.662%   $66.1045   $66.10   $66.10   $66.10  
  Purchase #2 $92.88   9.595%   $101.7918   $101.79   $101.80   $101.80  
  Purchase #3 $212.73   12.426%   $239.1638   $239.16   $239.15   $239.20  
  Purchase #4 $64.59   9.745%   $70.8843   $70.88   $70.90   $70.90  
  Purchase #5 $150.96   3.820%   $156.7267   $156.73   $156.75   $156.70  
  Purchase #6 $235.70   3.359%   $243.6172   $243.62   $243.60   $243.60  
  Purchase #7 $149.48   3.591%   $154.8478   $154.85   $154.85   $154.80  
  7 purchase totals = $967.74       $1,033.1361   $1,033.13   $1,033.15   $1,033.10