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 $93.27   3.734%   $96.7527   $96.75   $96.75   $96.80  
  Purchase #2 $32.36   9.226%   $35.3455   $35.35   $35.35   $35.30  
  Purchase #3 $234.39   4.199%   $244.232   $244.23   $244.25   $244.20  
  Purchase #4 $233.29   11.696%   $260.5756   $260.58   $260.60   $260.60  
  Purchase #5 $152.46   8.443%   $165.3322   $165.33   $165.35   $165.30  
  Purchase #6 $63.44   3.355%   $65.5684   $65.57   $65.55   $65.60  
  Purchase #7 $116.55   10.577%   $128.8775   $128.88   $128.90   $128.90  
  7 purchase totals = $925.76       $996.6839   $996.69   $996.75   $996.70