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 $56.52   7.821%   $60.9404   $60.94   $60.95   $60.90  
  Purchase #2 $50.29   3.514%   $52.0572   $52.06   $52.05   $52.10  
  Purchase #3 $194.43   9.523%   $212.9456   $212.95   $212.95   $212.90  
  Purchase #4 $214.29   9.652%   $234.9733   $234.97   $234.95   $235.00  
  Purchase #5 $250.34   7.662%   $269.5211   $269.52   $269.50   $269.50  
  Purchase #6 $105.92   10.304%   $116.834   $116.83   $116.85   $116.80  
  Purchase #7 $78.71   9.362%   $86.0788   $86.08   $86.10   $86.10  
  7 purchase totals = $950.50       $1,033.3504   $1,033.35   $1,033.35   $1,033.30