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 $237.81   11.312%   $264.7111   $264.71   $264.70   $264.70  
  Purchase #2 $124.45   5.769%   $131.6295   $131.63   $131.65   $131.60  
  Purchase #3 $235.31   13.335%   $266.6886   $266.69   $266.70   $266.70  
  Purchase #4 $44.81   5.640%   $47.3373   $47.34   $47.35   $47.30  
  Purchase #5 $240.99   5.698%   $254.7216   $254.72   $254.70   $254.70  
  Purchase #6 $183.58   7.773%   $197.8497   $197.85   $197.85   $197.80  
  Purchase #7 $12.80   9.494%   $14.0152   $14.02   $14.00   $14.00  
  7 purchase totals = $1,079.75       $1,176.9530   $1,176.96   $1,176.95   $1,176.80