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 $59.68   7.814%   $64.3434   $64.34   $64.35   $64.30  
  Purchase #2 $209.69   11.771%   $234.3726   $234.37   $234.35   $234.40  
  Purchase #3 $155.65   13.374%   $176.4666   $176.47   $176.45   $176.50  
  Purchase #4 $77.31   5.568%   $81.6146   $81.61   $81.60   $81.60  
  Purchase #5 $160.53   5.451%   $169.2805   $169.28   $169.30   $169.30  
  Purchase #6 $61.46   13.659%   $69.8548   $69.85   $69.85   $69.90  
  Purchase #7 $240.28   5.364%   $253.1686   $253.17   $253.15   $253.20  
  7 purchase totals = $964.60       $1,049.1011   $1,049.09   $1,049.05   $1,049.20