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 $207.51   12.196%   $232.8179   $232.82   $232.80   $232.80  
  Purchase #2 $101.88   12.735%   $114.8544   $114.85   $114.85   $114.90  
  Purchase #3 $69.64   7.675%   $74.9849   $74.98   $75.00   $75.00  
  Purchase #4 $34.69   5.146%   $36.4751   $36.48   $36.50   $36.50  
  Purchase #5 $186.54   6.107%   $197.932   $197.93   $197.95   $197.90  
  Purchase #6 $150.58   4.538%   $157.4133   $157.41   $157.40   $157.40  
  Purchase #7 $231.93   10.401%   $256.053   $256.05   $256.05   $256.10  
  7 purchase totals = $982.77       $1,070.5306   $1,070.52   $1,070.55   $1,070.60