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 $189.73   9.595%   $207.9346   $207.93   $207.95   $207.90  
  Purchase #2 $44.60   13.757%   $50.7356   $50.74   $50.75   $50.70  
  Purchase #3 $53.98   8.343%   $58.4836   $58.48   $58.50   $58.50  
  Purchase #4 $204.78   7.233%   $219.5917   $219.59   $219.60   $219.60  
  Purchase #5 $219.70   8.487%   $238.3459   $238.35   $238.35   $238.30  
  Purchase #6 $193.26   3.273%   $199.5854   $199.59   $199.60   $199.60  
  Purchase #7 $47.64   9.127%   $51.9881   $51.99   $52.00   $52.00  
  7 purchase totals = $953.69       $1,026.6649   $1,026.67   $1,026.75   $1,026.60