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 $61.73   8.436%   $66.9375   $66.94   $66.95   $66.90  
  Purchase #2 $139.30   6.179%   $147.9073   $147.91   $147.90   $147.90  
  Purchase #3 $192.27   7.854%   $207.3709   $207.37   $207.35   $207.40  
  Purchase #4 $245.89   8.392%   $266.5251   $266.53   $266.55   $266.50  
  Purchase #5 $241.39   9.759%   $264.9473   $264.95   $264.95   $264.90  
  Purchase #6 $127.35   6.485%   $135.6086   $135.61   $135.60   $135.60  
  Purchase #7 $41.50   10.257%   $45.7567   $45.76   $45.75   $45.80  
  7 purchase totals = $1,049.43       $1,135.0534   $1,135.07   $1,135.05   $1,135.00