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 $211.49   13.830%   $240.7391   $240.74   $240.75   $240.70  
  Purchase #2 $54.51   3.605%   $56.4751   $56.48   $56.50   $56.50  
  Purchase #3 $64.89   4.873%   $68.0521   $68.05   $68.05   $68.10  
  Purchase #4 $237.67   4.642%   $248.7026   $248.70   $248.70   $248.70  
  Purchase #5 $79.32   11.751%   $88.6409   $88.64   $88.65   $88.60  
  Purchase #6 $158.61   6.561%   $169.0164   $169.02   $169.00   $169.00  
  Purchase #7 $150.45   7.151%   $161.2087   $161.21   $161.20   $161.20  
  7 purchase totals = $956.94       $1,032.8349   $1,032.84   $1,032.85   $1,032.80