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 $195.64   5.517%   $206.4335   $206.43   $206.45   $206.40  
  Purchase #2 $82.43   7.393%   $88.524   $88.52   $88.50   $88.50  
  Purchase #3 $221.43   3.495%   $229.169   $229.17   $229.15   $229.20  
  Purchase #4 $216.28   5.102%   $227.3146   $227.31   $227.30   $227.30  
  Purchase #5 $241.50   10.492%   $266.8382   $266.84   $266.85   $266.80  
  Purchase #6 $119.61   7.854%   $129.0042   $129.00   $129.00   $129.00  
  Purchase #7 $237.97   10.608%   $263.2139   $263.21   $263.20   $263.20  
  7 purchase totals = $1,314.86       $1,410.4974   $1,410.48   $1,410.45   $1,410.40