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 $244.90   10.159%   $269.7794   $269.78   $269.80   $269.80  
  Purchase #2 $5.73   10.515%   $6.3325   $6.33   $6.35   $6.30  
  Purchase #3 $83.48   7.776%   $89.9714   $89.97   $89.95   $90.00  
  Purchase #4 $210.73   12.321%   $236.694   $236.69   $236.70   $236.70  
  Purchase #5 $101.64   12.846%   $114.6967   $114.70   $114.70   $114.70  
  Purchase #6 $38.52   4.687%   $40.3254   $40.33   $40.35   $40.30  
  Purchase #7 $234.42   8.321%   $253.9261   $253.93   $253.95   $253.90  
  7 purchase totals = $919.42       $1,011.7255   $1,011.73   $1,011.80   $1,011.70