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 $104.35   11.122%   $115.9558   $115.96   $115.95   $116.00  
  Purchase #2 $33.41   13.754%   $38.0052   $38.01   $38.00   $38.00  
  Purchase #3 $78.52   7.587%   $84.4773   $84.48   $84.50   $84.50  
  Purchase #4 $61.30   7.675%   $66.0048   $66.00   $66.00   $66.00  
  Purchase #5 $174.63   9.603%   $191.3997   $191.40   $191.40   $191.40  
  Purchase #6 $55.64   9.317%   $60.824   $60.82   $60.80   $60.80  
  Purchase #7 $169.74   4.269%   $176.9862   $176.99   $177.00   $177.00  
  7 purchase totals = $677.59       $733.6530   $733.66   $733.65   $733.70