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 $61.34   8.239%   $66.3938   $66.39   $66.40   $66.40  
  Purchase #2 $150.92   6.550%   $160.8053   $160.81   $160.80   $160.80  
  Purchase #3 $34.64   5.175%   $36.4326   $36.43   $36.45   $36.40  
  Purchase #4 $226.46   10.102%   $249.337   $249.34   $249.35   $249.30  
  Purchase #5 $248.73   5.728%   $262.9773   $262.98   $263.00   $263.00  
  Purchase #6 $246.37   11.199%   $273.961   $273.96   $273.95   $274.00  
  Purchase #7 $234.40   7.840%   $252.777   $252.78   $252.80   $252.80  
  7 purchase totals = $1,202.86       $1,302.6840   $1,302.69   $1,302.75   $1,302.70