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 $55.66   13.740%   $63.3077   $63.31   $63.30   $63.30  
  Purchase #2 $223.78   3.103%   $230.7239   $230.72   $230.70   $230.70  
  Purchase #3 $114.65   10.535%   $126.7284   $126.73   $126.75   $126.70  
  Purchase #4 $179.90   8.308%   $194.8461   $194.85   $194.85   $194.80  
  Purchase #5 $227.77   3.272%   $235.2226   $235.22   $235.20   $235.20  
  Purchase #6 $28.73   4.237%   $29.9473   $29.95   $29.95   $29.90  
  Purchase #7 $122.57   4.142%   $127.6468   $127.65   $127.65   $127.60  
  7 purchase totals = $953.06       $1,008.4228   $1,008.43   $1,008.40   $1,008.20