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 $56.84   13.748%   $64.6544   $64.65   $64.65   $64.70  
  Purchase #2 $250.58   7.523%   $269.4311   $269.43   $269.45   $269.40  
  Purchase #3 $190.33   8.255%   $206.0417   $206.04   $206.05   $206.00  
  Purchase #4 $65.38   6.184%   $69.4231   $69.42   $69.40   $69.40  
  Purchase #5 $236.67   4.290%   $246.8231   $246.82   $246.80   $246.80  
  Purchase #6 $39.52   4.395%   $41.2569   $41.26   $41.25   $41.30  
  Purchase #7 $213.99   9.582%   $234.4945   $234.49   $234.50   $234.50  
  7 purchase totals = $1,053.31       $1,132.1248   $1,132.11   $1,132.10   $1,132.10