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 $159.32   10.862%   $176.6253   $176.63   $176.65   $176.60  
  Purchase #2 $72.88   6.331%   $77.494   $77.49   $77.50   $77.50  
  Purchase #3 $63.52   6.433%   $67.6062   $67.61   $67.60   $67.60  
  Purchase #4 $196.57   5.136%   $206.6658   $206.67   $206.65   $206.70  
  Purchase #5 $234.41   8.371%   $254.0325   $254.03   $254.05   $254.00  
  Purchase #6 $207.68   8.596%   $225.5322   $225.53   $225.55   $225.50  
  Purchase #7 $240.30   3.188%   $247.9608   $247.96   $247.95   $248.00  
  7 purchase totals = $1,174.68       $1,255.9168   $1,255.92   $1,255.95   $1,255.90