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 $61.68   6.795%   $65.8712   $65.87   $65.85   $65.90  
  Purchase #2 $232.33   13.746%   $264.2661   $264.27   $264.25   $264.30  
  Purchase #3 $46.85   5.445%   $49.401   $49.40   $49.40   $49.40  
  Purchase #4 $153.52   5.795%   $162.4165   $162.42   $162.40   $162.40  
  Purchase #5 $176.98   4.651%   $185.2113   $185.21   $185.20   $185.20  
  Purchase #6 $193.58   5.116%   $203.4836   $203.48   $203.50   $203.50  
  Purchase #7 $7.28   11.123%   $8.0898   $8.09   $8.10   $8.10  
  7 purchase totals = $872.22       $938.7395   $938.74   $938.70   $938.80