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 $236.71   10.158%   $260.755   $260.76   $260.75   $260.80  
  Purchase #2 $245.74   13.335%   $278.5094   $278.51   $278.50   $278.50  
  Purchase #3 $57.69   13.627%   $65.5514   $65.55   $65.55   $65.60  
  Purchase #4 $42.33   12.260%   $47.5197   $47.52   $47.50   $47.50  
  Purchase #5 $147.69   10.553%   $163.2757   $163.28   $163.30   $163.30  
  Purchase #6 $247.26   9.181%   $269.9609   $269.96   $269.95   $270.00  
  Purchase #7 $36.86   7.737%   $39.7119   $39.71   $39.70   $39.70  
  7 purchase totals = $1,014.28       $1,125.2840   $1,125.29   $1,125.25   $1,125.40