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 $247.96   5.204%   $260.8638   $260.86   $260.85   $260.90  
  Purchase #2 $213.88   5.355%   $225.3333   $225.33   $225.35   $225.30  
  Purchase #3 $128.50   4.693%   $134.5305   $134.53   $134.55   $134.50  
  Purchase #4 $48.69   7.760%   $52.4683   $52.47   $52.45   $52.50  
  Purchase #5 $213.73   8.726%   $232.3801   $232.38   $232.40   $232.40  
  Purchase #6 $146.38   11.831%   $163.6982   $163.70   $163.70   $163.70  
  Purchase #7 $206.99   11.363%   $230.5103   $230.51   $230.50   $230.50  
  7 purchase totals = $1,206.13       $1,299.7845   $1,299.78   $1,299.80   $1,299.80