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 $81.69   6.286%   $86.825   $86.83   $86.85   $86.80  
  Purchase #2 $141.79   7.519%   $152.4512   $152.45   $152.45   $152.50  
  Purchase #3 $108.80   11.212%   $120.9987   $121.00   $121.00   $121.00  
  Purchase #4 $65.46   5.301%   $68.93   $68.93   $68.95   $68.90  
  Purchase #5 $13.57   8.726%   $14.7541   $14.75   $14.75   $14.80  
  Purchase #6 $56.64   11.845%   $63.349   $63.35   $63.35   $63.30  
  Purchase #7 $52.26   11.639%   $58.3425   $58.34   $58.35   $58.30  
  7 purchase totals = $520.21       $565.6505   $565.65   $565.70   $565.60