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 $61.41   11.376%   $68.396   $68.40   $68.40   $68.40  
  Purchase #2 $155.35   9.333%   $169.8488   $169.85   $169.85   $169.80  
  Purchase #3 $138.27   9.622%   $151.5743   $151.57   $151.55   $151.60  
  Purchase #4 $165.47   6.710%   $176.573   $176.57   $176.55   $176.60  
  Purchase #5 $215.74   5.423%   $227.4396   $227.44   $227.45   $227.40  
  Purchase #6 $102.43   6.142%   $108.7213   $108.72   $108.70   $108.70  
  Purchase #7 $157.88   7.867%   $170.3004   $170.30   $170.30   $170.30  
  7 purchase totals = $996.55       $1,072.8534   $1,072.85   $1,072.80   $1,072.80