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 $66.46   8.311%   $71.9835   $71.98   $72.00   $72.00  
  Purchase #2 $183.62   12.651%   $206.8498   $206.85   $206.85   $206.80  
  Purchase #3 $74.96   7.494%   $80.5775   $80.58   $80.60   $80.60  
  Purchase #4 $116.66   10.542%   $128.9583   $128.96   $128.95   $129.00  
  Purchase #5 $51.42   9.445%   $56.2766   $56.28   $56.30   $56.30  
  Purchase #6 $194.93   3.373%   $201.505   $201.51   $201.50   $201.50  
  Purchase #7 $74.60   3.211%   $76.9954   $77.00   $77.00   $77.00  
  7 purchase totals = $762.65       $823.1461   $823.16   $823.20   $823.20