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 $146.96   9.590%   $161.0535   $161.05   $161.05   $161.10  
  Purchase #2 $84.62   5.709%   $89.451   $89.45   $89.45   $89.50  
  Purchase #3 $144.82   8.613%   $157.2933   $157.29   $157.30   $157.30  
  Purchase #4 $175.89   9.170%   $192.0191   $192.02   $192.00   $192.00  
  Purchase #5 $233.86   9.838%   $256.8671   $256.87   $256.85   $256.90  
  Purchase #6 $28.57   4.214%   $29.7739   $29.77   $29.75   $29.80  
  Purchase #7 $102.35   11.571%   $114.1929   $114.19   $114.20   $114.20  
  7 purchase totals = $917.07       $1,000.6508   $1,000.64   $1,000.60   $1,000.80